The purpose of local_lock_t is to abstract: preempt_disable() /
local_bh_disable() / local_irq_disable(). These are the traditional
means of gaining access to per-cpu data, but are fundamentally
non-preemptible.
local_lock_t provides a per-cpu lock, that on !PREEMPT_RT reduces to
no-ops, just like regular spinlocks do on UP.
This gives rise to:
CPU0 CPU1
local_lock(B) spin_lock_irq(A)
<IRQ>
spin_lock(A) local_lock(B)
Where lockdep then figures things will lock up; which would be true if
B were any other kind of lock. However this is a false positive, no
such deadlock actually exists.
For !RT the above local_lock(B) is preempt_disable(), and there's
obviously no deadlock; alternatively, CPU0's B != CPU1's B.
For RT the argument is that since local_lock() nests inside
spin_lock(), it cannot be used in hardirq context, and therefore CPU0
cannot in fact happen. Even though B is a real lock, it is a
preemptible lock and any threaded-irq would simply schedule out and
let the preempted task (which holds B) continue such that the task on
CPU1 can make progress, after which the threaded-irq resumes and can
finish.
This means that we can never form an IRQ inversion on a local_lock
dependency, so terminate the graph walk when looking for IRQ
inversions when we encounter one.
One consequence is that (for LOCKDEP_SMALL) when we look for redundant
dependencies, A -> B is not redundant in the presence of A -> L -> B.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
[peterz: Changelog]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
In preparation for adding an TRACE_IRQFLAGS dependent skip function to
check_redundant(), move it below the TRACE_IRQFLAGS #ifdef.
While there, provide a stub function to reduce #ifdef usage.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Some __bfs() walks will have additional iteration constraints (beyond
the path being strong). Provide an additional function to allow
terminating graph walks.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
The local_lock_t's are special, because they cannot form IRQ
inversions, make sure we can tell them apart from the rest of the
locks.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
When the compiler doesn't feel like inlining, it causes a noinstr
fail:
vmlinux.o: warning: objtool: lock_is_held_type()+0xb: call to lockdep_enabled() leaves .noinstr.text section
Fixes: 4d004099a6 ("lockdep: Fix lockdep recursion")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210106144017.592595176@infradead.org
- A few extensions to the rwsem API and support for opportunistic
spinning and lock stealing
- lockdep selftest improvements
- Documentation updates
- Cleanups and small fixes all over the place
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Merge tag 'locking-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Thomas Gleixner:
"A moderate set of locking updates:
- A few extensions to the rwsem API and support for opportunistic
spinning and lock stealing
- lockdep selftest improvements
- Documentation updates
- Cleanups and small fixes all over the place"
* tag 'locking-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (21 commits)
seqlock: kernel-doc: Specify when preemption is automatically altered
seqlock: Prefix internal seqcount_t-only macros with a "do_"
Documentation: seqlock: s/LOCKTYPE/LOCKNAME/g
locking/rwsem: Remove reader optimistic spinning
locking/rwsem: Enable reader optimistic lock stealing
locking/rwsem: Prevent potential lock starvation
locking/rwsem: Pass the current atomic count to rwsem_down_read_slowpath()
locking/rwsem: Fold __down_{read,write}*()
locking/rwsem: Introduce rwsem_write_trylock()
locking/rwsem: Better collate rwsem_read_trylock()
rwsem: Implement down_read_interruptible
rwsem: Implement down_read_killable_nested
refcount: Fix a kernel-doc markup
completion: Drop init_completion define
atomic: Update MAINTAINERS
atomic: Delete obsolete documentation
seqlock: Rename __seqprop() users
lockdep/selftest: Add spin_nest_lock test
lockdep/selftests: Fix PROVE_RAW_LOCK_NESTING
seqlock: avoid -Wshadow warnings
...
RCU:
- Avoid cpuinfo-induced IPI pileups and idle-CPU IPIs.
- Lockdep-RCU updates reducing the need for __maybe_unused.
- Tasks-RCU updates.
- Miscellaneous fixes.
- Documentation updates.
- Torture-test updates.
KCSAN:
- updates for selftests, avoiding setting watchpoints on NULL pointers
- fix to watchpoint encoding
LKMM:
- updates for documentation along with some updates to example-code
litmus tests
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Merge tag 'core-rcu-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull RCU updates from Thomas Gleixner:
"RCU, LKMM and KCSAN updates collected by Paul McKenney.
RCU:
- Avoid cpuinfo-induced IPI pileups and idle-CPU IPIs
- Lockdep-RCU updates reducing the need for __maybe_unused
- Tasks-RCU updates
- Miscellaneous fixes
- Documentation updates
- Torture-test updates
KCSAN:
- updates for selftests, avoiding setting watchpoints on NULL pointers
- fix to watchpoint encoding
LKMM:
- updates for documentation along with some updates to example-code
litmus tests"
* tag 'core-rcu-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (72 commits)
srcu: Take early exit on memory-allocation failure
rcu/tree: Defer kvfree_rcu() allocation to a clean context
rcu: Do not report strict GPs for outgoing CPUs
rcu: Fix a typo in rcu_blocking_is_gp() header comment
rcu: Prevent lockdep-RCU splats on lock acquisition/release
rcu/tree: nocb: Avoid raising softirq for offloaded ready-to-execute CBs
rcu,ftrace: Fix ftrace recursion
rcu/tree: Make struct kernel_param_ops definitions const
rcu/tree: Add a warning if CPU being onlined did not report QS already
rcu: Clarify nocb kthreads naming in RCU_NOCB_CPU config
rcu: Fix single-CPU check in rcu_blocking_is_gp()
rcu: Implement rcu_segcblist_is_offloaded() config dependent
list.h: Update comment to explicitly note circular lists
rcu: Panic after fixed number of stalls
x86/smpboot: Move rcu_cpu_starting() earlier
rcu: Allow rcu_irq_enter_check_tick() from NMI
tools/memory-model: Label MP tests' producers and consumers
tools/memory-model: Use "buf" and "flag" for message-passing tests
tools/memory-model: Add types to litmus tests
tools/memory-model: Add a glossary of LKMM terms
...
Reader optimistic spinning is helpful when the reader critical section
is short and there aren't that many readers around. It also improves
the chance that a reader can get the lock as writer optimistic spinning
disproportionally favors writers much more than readers.
Since commit d3681e269f ("locking/rwsem: Wake up almost all readers
in wait queue"), all the waiting readers are woken up so that they can
all get the read lock and run in parallel. When the number of contending
readers is large, allowing reader optimistic spinning will likely cause
reader fragmentation where multiple smaller groups of readers can get
the read lock in a sequential manner separated by writers. That reduces
reader parallelism.
One possible way to address that drawback is to limit the number of
readers (preferably one) that can do optimistic spinning. These readers
act as representatives of all the waiting readers in the wait queue as
they will wake up all those waiting readers once they get the lock.
Alternatively, as reader optimistic lock stealing has already enhanced
fairness to readers, it may be easier to just remove reader optimistic
spinning and simplifying the optimistic spinning code as a result.
Performance measurements (locking throughput kops/s) using a locking
microbenchmark with 50/50 reader/writer distribution and turbo-boost
disabled was done on a 2-socket Cascade Lake system (48-core 96-thread)
to see the impacts of these changes:
1) Vanilla - 5.10-rc3 kernel
2) Before - 5.10-rc3 kernel with previous patches in this series
2) limit-rspin - 5.10-rc3 kernel with limited reader spinning patch
3) no-rspin - 5.10-rc3 kernel with reader spinning disabled
# of threads CS Load Vanilla Before limit-rspin no-rspin
------------ ------- ------- ------ ----------- --------
2 1 5,185 5,662 5,214 5,077
4 1 5,107 4,983 5,188 4,760
8 1 4,782 4,564 4,720 4,628
16 1 4,680 4,053 4,567 3,402
32 1 4,299 1,115 1,118 1,098
64 1 3,218 983 1,001 957
96 1 1,938 944 957 930
2 20 2,008 2,128 2,264 1,665
4 20 1,390 1,033 1,046 1,101
8 20 1,472 1,155 1,098 1,213
16 20 1,332 1,077 1,089 1,122
32 20 967 914 917 980
64 20 787 874 891 858
96 20 730 836 847 844
2 100 372 356 360 355
4 100 492 425 434 392
8 100 533 537 529 538
16 100 548 572 568 598
32 100 499 520 527 537
64 100 466 517 526 512
96 100 406 497 506 509
The column "CS Load" represents the number of pause instructions issued
in the locking critical section. A CS load of 1 is extremely short and
is not likey in real situations. A load of 20 (moderate) and 100 (long)
are more realistic.
It can be seen that the previous patches in this series have reduced
performance in general except in highly contended cases with moderate
or long critical sections that performance improves a bit. This change
is mostly caused by the "Prevent potential lock starvation" patch that
reduce reader optimistic spinning and hence reduce reader fragmentation.
The patch that further limit reader optimistic spinning doesn't seem to
have too much impact on overall performance as shown in the benchmark
data.
The patch that disables reader optimistic spinning shows reduced
performance at lightly loaded cases, but comparable or slightly better
performance on with heavier contention.
This patch just removes reader optimistic spinning for now. As readers
are not going to do optimistic spinning anymore, we don't need to
consider if the OSQ is empty or not when doing lock stealing.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lkml.kernel.org/r/20201121041416.12285-6-longman@redhat.com
If the optimistic spinning queue is empty and the rwsem does not have
the handoff or write-lock bits set, it is actually not necessary to
call rwsem_optimistic_spin() to spin on it. Instead, it can steal the
lock directly as its reader bias is in the count already. If it is
the first reader in this state, it will try to wake up other readers
in the wait queue.
With this patch applied, the following were the lock event counts
after rebooting a 2-socket system and a "make -j96" kernel rebuild.
rwsem_opt_rlock=4437
rwsem_rlock=29
rwsem_rlock_steal=19
So lock stealing represents about 0.4% of all the read locks acquired
in the slow path.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lkml.kernel.org/r/20201121041416.12285-4-longman@redhat.com
The lock handoff bit is added in commit 4f23dbc1e6 ("locking/rwsem:
Implement lock handoff to prevent lock starvation") to avoid lock
starvation. However, allowing readers to do optimistic spinning does
introduce an unlikely scenario where lock starvation can happen.
The lock handoff bit may only be set when a waiter is being woken up.
In the case of reader unlock, wakeup happens only when the reader count
reaches 0. If there is a continuous stream of incoming readers acquiring
read lock via optimistic spinning, it is possible that the reader count
may never reach 0 and so the handoff bit will never be asserted.
One way to prevent this scenario from happening is to disallow optimistic
spinning if the rwsem is currently owned by readers. If the previous
or current owner is a writer, optimistic spinning will be allowed.
If the previous owner is a reader but the reader count has reached 0
before, a wakeup should have been issued. So the handoff mechanism
will be kicked in to prevent lock starvation. As a result, it should
be OK to do optimistic spinning in this case.
This patch may have some impact on reader performance as it reduces
reader optimistic spinning especially if the lock critical sections
are short the number of contending readers are small.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lkml.kernel.org/r/20201121041416.12285-3-longman@redhat.com
The atomic count value right after reader count increment can be useful
to determine the rwsem state at trylock time. So the count value is
passed down to rwsem_down_read_slowpath() to be used when appropriate.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lkml.kernel.org/r/20201121041416.12285-2-longman@redhat.com
In preparation for converting exec_update_mutex to a rwsem so that
multiple readers can execute in parallel and not deadlock, add
down_read_interruptible. This is needed for perf_event_open to be
converted (with no semantic changes) from working on a mutex to
wroking on a rwsem.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/87k0tybqfy.fsf@x220.int.ebiederm.org
In preparation for converting exec_update_mutex to a rwsem so that
multiple readers can execute in parallel and not deadlock, add
down_read_killable_nested. This is needed so that kcmp_lock
can be converted from working on a mutexes to working on rw_semaphores.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/87o8jabqh3.fsf@x220.int.ebiederm.org
A warning was hit when running xfstests/generic/068 in a Hyper-V guest:
[...] ------------[ cut here ]------------
[...] DEBUG_LOCKS_WARN_ON(lockdep_hardirqs_enabled())
[...] WARNING: CPU: 2 PID: 1350 at kernel/locking/lockdep.c:5280 check_flags.part.0+0x165/0x170
[...] ...
[...] Workqueue: events pwq_unbound_release_workfn
[...] RIP: 0010:check_flags.part.0+0x165/0x170
[...] ...
[...] Call Trace:
[...] lock_is_held_type+0x72/0x150
[...] ? lock_acquire+0x16e/0x4a0
[...] rcu_read_lock_sched_held+0x3f/0x80
[...] __send_ipi_one+0x14d/0x1b0
[...] hv_send_ipi+0x12/0x30
[...] __pv_queued_spin_unlock_slowpath+0xd1/0x110
[...] __raw_callee_save___pv_queued_spin_unlock_slowpath+0x11/0x20
[...] .slowpath+0x9/0xe
[...] lockdep_unregister_key+0x128/0x180
[...] pwq_unbound_release_workfn+0xbb/0xf0
[...] process_one_work+0x227/0x5c0
[...] worker_thread+0x55/0x3c0
[...] ? process_one_work+0x5c0/0x5c0
[...] kthread+0x153/0x170
[...] ? __kthread_bind_mask+0x60/0x60
[...] ret_from_fork+0x1f/0x30
The cause of the problem is we have call chain lockdep_unregister_key()
-> <irq disabled by raw_local_irq_save()> lockdep_unlock() ->
arch_spin_unlock() -> __pv_queued_spin_unlock_slowpath() -> pv_kick() ->
__send_ipi_one() -> trace_hyperv_send_ipi_one().
Although this particular warning is triggered because Hyper-V has a
trace point in ipi sending, but in general arch_spin_unlock() may call
another function having a trace point in it, so put the arch_spin_lock()
and arch_spin_unlock() after lock_recursion protection to fix this
problem and avoid similiar problems.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201113110512.1056501-1-boqun.feng@gmail.com
Chris Wilson reported a problem spotted by check_chain_key(): a chain
key got changed in validate_chain() because we modify the ->read in
validate_chain() to skip checks for dependency adding, and ->read is
taken into calculation for chain key since commit f611e8cf98
("lockdep: Take read/write status in consideration when generate
chainkey").
Fix this by avoiding to modify ->read in validate_chain() based on two
facts: a) since we now support recursive read lock detection, there is
no need to skip checks for dependency adding for recursive readers, b)
since we have a), there is only one case left (nest_lock) where we want
to skip checks in validate_chain(), we simply remove the modification
for ->read and rely on the return value of check_deadlock() to skip the
dependency adding.
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201102053743.450459-1-boqun.feng@gmail.com
When executing the LOCK06 locktorture scenario featuring percpu-rwsem,
the RCU callback rcu_sync_func() may still be pending after locktorture
module is removed. This can in turn lead to the following Oops:
BUG: unable to handle page fault for address: ffffffffc00eb920
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 6500a067 P4D 6500a067 PUD 6500c067 PMD 13a36c067 PTE 800000013691c163
Oops: 0000 [#1] PREEMPT SMP
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.9.0-rc5+ #4
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
RIP: 0010:rcu_cblist_dequeue+0x12/0x30
Call Trace:
<IRQ>
rcu_core+0x1b1/0x860
__do_softirq+0xfe/0x326
asm_call_on_stack+0x12/0x20
</IRQ>
do_softirq_own_stack+0x5f/0x80
irq_exit_rcu+0xaf/0xc0
sysvec_apic_timer_interrupt+0x2e/0xb0
asm_sysvec_apic_timer_interrupt+0x12/0x20
This commit avoids tis problem by adding an exit hook in lock_torture_ops
and using it to call percpu_free_rwsem() for percpu rwsem torture during
the module-cleanup function, thus ensuring that rcu_sync_func() completes
before module exits.
It is also necessary to call the exit hook if lock_torture_init()
fails half-way, so this commit also adds an ->init_called field in
lock_torture_cxt to indicate that exit hook, if present, must be called.
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
If an locktorture torture-test run is given a bad kvm.sh argument, the
test will complain to the console, which is good. What is bad is that
from the user's perspective, it will just hang for the time specified
by the --duration argument. This commit therefore forces an immediate
kernel shutdown if a lock_torture_init()-time error occurs, thus avoiding
the appearance of a hang. It also forces a console splat in this case
to clearly indicate the presence of an error.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Exclusive locks do not have readlock support, which means that a
locktorture run with the following module parameters will do nothing:
torture_type=mutex_lock nwriters_stress=0 nreaders_stress=1
This commit therefore rejects this combination for exclusive locks by
returning -EINVAL during module init.
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a last_lock_release variable that tracks the time of
the last ->writeunlock() call, which allows easier diagnosing of lock
hangs when using a kernel debugger.
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
- Fix incorrect failure injection handling on the fuxtex code
- Prevent a preemption warning in lockdep when tracking local_irq_enable()
and interrupts are already enabled
- Remove more raw_cpu_read() usage from lockdep which causes state
corruption on !X86 architectures.
- Make the nr_unused_locks accounting in lockdep correct again.
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Merge tag 'locking-urgent-2020-11-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking fixes from Thomas Gleixner:
"A couple of locking fixes:
- Fix incorrect failure injection handling in the fuxtex code
- Prevent a preemption warning in lockdep when tracking
local_irq_enable() and interrupts are already enabled
- Remove more raw_cpu_read() usage from lockdep which causes state
corruption on !X86 architectures.
- Make the nr_unused_locks accounting in lockdep correct again"
* tag 'locking-urgent-2020-11-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
lockdep: Fix nr_unused_locks accounting
locking/lockdep: Remove more raw_cpu_read() usage
futex: Fix incorrect should_fail_futex() handling
lockdep: Fix preemption WARN for spurious IRQ-enable
Chris reported that commit 24d5a3bffef1 ("lockdep: Fix
usage_traceoverflow") breaks the nr_unused_locks validation code
triggered by /proc/lockdep_stats.
By fully splitting LOCK_USED and LOCK_USED_READ it becomes a bad
indicator for accounting nr_unused_locks; simplyfy by using any first
bit.
Fixes: 24d5a3bffef1 ("lockdep: Fix usage_traceoverflow")
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://lkml.kernel.org/r/20201027124834.GL2628@hirez.programming.kicks-ass.net
I initially thought raw_cpu_read() was OK, since if it is !0 we have
IRQs disabled and can't get migrated, so if we get migrated both CPUs
must have 0 and it doesn't matter which 0 we read.
And while that is true; it isn't the whole store, on pretty much all
architectures (except x86) this can result in computing the address for
one CPU, getting migrated, the old CPU continuing execution with another
task (possibly setting recursion) and then the new CPU reading the value
of the old CPU, which is no longer 0.
Similer to:
baffd723e4 ("lockdep: Revert "lockdep: Use raw_cpu_*() for per-cpu variables"")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201026152256.GB2651@hirez.programming.kicks-ass.net
It is valid (albeit uncommon) to call local_irq_enable() without first
having called local_irq_disable(). In this case we enter
lockdep_hardirqs_on*() with IRQs enabled and trip a preemption warning
for using __this_cpu_read().
Use this_cpu_read() instead to avoid the warning.
Fixes: 4d004099a6 ("lockdep: Fix lockdep recursion")
Reported-by: syzbot+53f8ce8bbc07924b6417@syzkaller.appspotmail.com
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Pull RCU changes from Ingo Molnar:
- Debugging for smp_call_function()
- RT raw/non-raw lock ordering fixes
- Strict grace periods for KASAN
- New smp_call_function() torture test
- Torture-test updates
- Documentation updates
- Miscellaneous fixes
[ This doesn't actually pull the tag - I've dropped the last merge from
the RCU branch due to questions about the series. - Linus ]
* tag 'core-rcu-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (77 commits)
smp: Make symbol 'csd_bug_count' static
kernel/smp: Provide CSD lock timeout diagnostics
smp: Add source and destination CPUs to __call_single_data
rcu: Shrink each possible cpu krcp
rcu/segcblist: Prevent useless GP start if no CBs to accelerate
torture: Add gdb support
rcutorture: Allow pointer leaks to test diagnostic code
rcutorture: Hoist OOM registry up one level
refperf: Avoid null pointer dereference when buf fails to allocate
rcutorture: Properly synchronize with OOM notifier
rcutorture: Properly set rcu_fwds for OOM handling
torture: Add kvm.sh --help and update help message
rcutorture: Add CONFIG_PROVE_RCU_LIST to TREE05
torture: Update initrd documentation
rcutorture: Replace HTTP links with HTTPS ones
locktorture: Make function torture_percpu_rwsem_init() static
torture: document --allcpus argument added to the kvm.sh script
rcutorture: Output number of elapsed grace periods
rcutorture: Remove KCSAN stubs
rcu: Remove unused "cpu" parameter from rcu_report_qs_rdp()
...
Steve reported that lockdep_assert*irq*(), when nested inside lockdep
itself, will trigger a false-positive.
One example is the stack-trace code, as called from inside lockdep,
triggering tracing, which in turn calls RCU, which then uses
lockdep_assert_irqs_disabled().
Fixes: a21ee6055c ("lockdep: Change hardirq{s_enabled,_context} to per-cpu variables")
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Basically print_lock_class_header()'s for loop is out of sync with the
the size of of ->usage_traces[].
Also clean things up a bit while at it, to avoid such mishaps in the future.
Fixes: 23870f1227 ("locking/lockdep: Fix "USED" <- "IN-NMI" inversions")
Reported-by: Qian Cai <cai@redhat.com>
Debugged-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Qian Cai <cai@redhat.com>
Link: https://lkml.kernel.org/r/20200930094937.GE2651@hirez.programming.kicks-ass.net
Pull v5.10 RCU changes from Paul E. McKenney:
- Debugging for smp_call_function().
- Strict grace periods for KASAN. The point of this series is to find
RCU-usage bugs, so the corresponding new RCU_STRICT_GRACE_PERIOD
Kconfig option depends on both DEBUG_KERNEL and RCU_EXPERT, and is
further disabled by dfefault. Finally, the help text includes
a goodly list of scary caveats.
- New smp_call_function() torture test.
- Torture-test updates.
- Documentation updates.
- Miscellaneous fixes.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Qian Cai reported a BFS_EQUEUEFULL warning [1] after read recursive
deadlock detection merged into tip tree recently. Unlike the previous
lockep graph searching, which iterate every lock class (every node in
the graph) exactly once, the graph searching for read recurisve deadlock
detection needs to iterate every lock dependency (every edge in the
graph) once, as a result, the maximum memory cost of the circular queue
changes from O(V), where V is the number of lock classes (nodes or
vertices) in the graph, to O(E), where E is the number of lock
dependencies (edges), because every lock class or dependency gets
enqueued once in the BFS. Therefore we hit the BFS_EQUEUEFULL case.
However, actually we don't need to enqueue all dependencies for the BFS,
because every time we enqueue a dependency, we almostly enqueue all
other dependencies in the same dependency list ("almostly" is because
we currently check before enqueue, so if a dependency doesn't pass the
check stage we won't enqueue it, however, we can always do in reverse
ordering), based on this, we can only enqueue the first dependency from
a dependency list and every time we want to fetch a new dependency to
work, we can either:
1) fetch the dependency next to the current dependency in the
dependency list
or
2) if the dependency in 1) doesn't exist, fetch the dependency from
the queue.
With this approach, the "max bfs queue depth" for a x86_64_defconfig +
lockdep and selftest config kernel can get descreased from:
max bfs queue depth: 201
to (after apply this patch)
max bfs queue depth: 61
While I'm at it, clean up the code logic a little (e.g. directly return
other than set a "ret" value and goto the "exit" label).
[1]: https://lore.kernel.org/lkml/17343f6f7f2438fc376125384133c5ba70c2a681.camel@redhat.com/
Reported-by: Qian Cai <cai@redhat.com>
Reported-by: syzbot+62ebe501c1ce9a91f68c@syzkaller.appspotmail.com
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200917080210.108095-1-boqun.feng@gmail.com
The __this_cpu*() accessors are (in general) IRQ-unsafe which, given
that percpu-rwsem is a blocking primitive, should be just fine.
However, file_end_write() is used from IRQ context and will cause
load-store issues on architectures where the per-cpu accessors are not
natively irq-safe.
Fix it by using the IRQ-safe this_cpu_*() for operations on
read_count. This will generate more expensive code on a number of
platforms, which might cause a performance regression for some of the
other percpu-rwsem users.
If any such is reported, we can consider alternative solutions.
Fixes: 70fe2f4815 ("aio: fix freeze protection of aio writes")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lkml.kernel.org/r/20200915140750.137881-1-houtao1@huawei.com
During the LPC RCU BoF Paul asked how come the "USED" <- "IN-NMI"
detector doesn't trip over rcu_read_lock()'s lockdep annotation.
Looking into this I found a very embarrasing typo in
verify_lock_unused():
- if (!(class->usage_mask & LOCK_USED))
+ if (!(class->usage_mask & LOCKF_USED))
fixing that will indeed cause rcu_read_lock() to insta-splat :/
The above typo means that instead of testing for: 0x100 (1 <<
LOCK_USED), we test for 8 (LOCK_USED), which corresponds to (1 <<
LOCK_ENABLED_HARDIRQ).
So instead of testing for _any_ used lock, it will only match any lock
used with interrupts enabled.
The rcu_read_lock() annotation uses .check=0, which means it will not
set any of the interrupt bits and will thus never match.
In order to properly fix the situation and allow rcu_read_lock() to
correctly work, split LOCK_USED into LOCK_USED and LOCK_USED_READ and by
having .read users set USED_READ and test USED, pure read-recursive
locks are permitted.
Fixes: f6f48e1804 ("lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20200902160323.GK1362448@hirez.programming.kicks-ass.net
Currently, the chainkey of a lock chain is a hash sum of the class_idx
of all the held locks, the read/write status are not taken in to
consideration while generating the chainkey. This could result into a
problem, if we have:
P1()
{
read_lock(B);
lock(A);
}
P2()
{
lock(A);
read_lock(B);
}
P3()
{
lock(A);
write_lock(B);
}
, and P1(), P2(), P3() run one by one. And when running P2(), lockdep
detects such a lock chain A -> B is not a deadlock, then it's added in
the chain cache, and then when running P3(), even if it's a deadlock, we
could miss it because of the hit of chain cache. This could be confirmed
by self testcase "chain cached mixed R-L/L-W ".
To resolve this, we use concept "hlock_id" to generate the chainkey, the
hlock_id is a tuple (hlock->class_idx, hlock->read), which fits in a u16
type. With this, the chainkeys are different is the lock sequences have
the same locks but different read/write status.
Besides, since we use "hlock_id" to generate chainkeys, the chain_hlocks
array now store the "hlock_id"s rather than lock_class indexes.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-15-boqun.feng@gmail.com
Since we have all the fundamental to handle recursive read locks, we now
add them into the dependency graph.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-13-boqun.feng@gmail.com
Currently, in safe->unsafe detection, lockdep misses the fact that a
LOCK_ENABLED_IRQ_*_READ usage and a LOCK_USED_IN_IRQ_*_READ usage may
cause deadlock too, for example:
P1 P2
<irq disabled>
write_lock(l1); <irq enabled>
read_lock(l2);
write_lock(l2);
<in irq>
read_lock(l1);
Actually, all of the following cases may cause deadlocks:
LOCK_USED_IN_IRQ_* -> LOCK_ENABLED_IRQ_*
LOCK_USED_IN_IRQ_*_READ -> LOCK_ENABLED_IRQ_*
LOCK_USED_IN_IRQ_* -> LOCK_ENABLED_IRQ_*_READ
LOCK_USED_IN_IRQ_*_READ -> LOCK_ENABLED_IRQ_*_READ
To fix this, we need to 1) change the calculation of exclusive_mask() so
that READ bits are not dropped and 2) always call usage() in
mark_lock_irq() to check usage deadlocks, even when the new usage of the
lock is READ.
Besides, adjust usage_match() and usage_acculumate() to recursive read
lock changes.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-12-boqun.feng@gmail.com
check_redundant() will report redundancy if it finds a path could
replace the about-to-add dependency in the BFS search. With recursive
read lock changes, we certainly need to change the match function for
the check_redundant(), because the path needs to match not only the lock
class but also the dependency kinds. For example, if the about-to-add
dependency @prev -> @next is A -(SN)-> B, and we find a path A -(S*)->
.. -(*R)->B in the dependency graph with __bfs() (for simplicity, we can
also say we find an -(SR)-> path from A to B), we can not replace the
dependency with that path in the BFS search. Because the -(SN)->
dependency can make a strong path with a following -(S*)-> dependency,
however an -(SR)-> path cannot.
Further, we can replace an -(SN)-> dependency with a -(EN)-> path, that
means if we find a path which is stronger than or equal to the
about-to-add dependency, we can report the redundancy. By "stronger", it
means both the start and the end of the path are not weaker than the
start and the end of the dependency (E is "stronger" than S and N is
"stronger" than R), so that we can replace the dependency with that
path.
To make sure we find a path whose start point is not weaker than the
about-to-add dependency, we use a trick: the ->only_xr of the root
(start point) of __bfs() is initialized as @prev-> == 0, therefore if
@prev is E, __bfs() will pick only -(E*)-> for the first dependency,
otherwise, __bfs() can pick -(E*)-> or -(S*)-> for the first dependency.
To make sure we find a path whose end point is not weaker than the
about-to-add dependency, we replace the match function for __bfs()
check_redundant(), we check for the case that either @next is R
(anything is not weaker than it) or the end point of the path is N
(which is not weaker than anything).
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-11-boqun.feng@gmail.com
Currently, lockdep only has limit support for deadlock detection for
recursive read locks.
This patch support deadlock detection for recursive read locks. The
basic idea is:
We are about to add dependency B -> A in to the dependency graph, we use
check_noncircular() to find whether we have a strong dependency path
A -> .. -> B so that we have a strong dependency circle (a closed strong
dependency path):
A -> .. -> B -> A
, which doesn't have two adjacent dependencies as -(*R)-> L -(S*)->.
Since A -> .. -> B is already a strong dependency path, so if either
B -> A is -(E*)-> or A -> .. -> B is -(*N)->, the circle A -> .. -> B ->
A is strong, otherwise not. So we introduce a new match function
hlock_conflict() to replace the class_equal() for the deadlock check in
check_noncircular().
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-10-boqun.feng@gmail.com
The "match" parameter of __bfs() is used for checking whether we hit a
match in the search, therefore it should return a boolean value rather
than an integer for better readability.
This patch then changes the return type of the function parameter and the
match functions to bool.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-9-boqun.feng@gmail.com
Now we have four types of dependencies in the dependency graph, and not
all the pathes carry real dependencies (the dependencies that may cause
a deadlock), for example:
Given lock A and B, if we have:
CPU1 CPU2
============= ==============
write_lock(A); read_lock(B);
read_lock(B); write_lock(A);
(assuming read_lock(B) is a recursive reader)
then we have dependencies A -(ER)-> B, and B -(SN)-> A, and a
dependency path A -(ER)-> B -(SN)-> A.
In lockdep w/o recursive locks, a dependency path from A to A
means a deadlock. However, the above case is obviously not a
deadlock, because no one holds B exclusively, therefore no one
waits for the other to release B, so who get A first in CPU1 and
CPU2 will run non-blockingly.
As a result, dependency path A -(ER)-> B -(SN)-> A is not a
real/strong dependency that could cause a deadlock.
From the observation above, we know that for a dependency path to be
real/strong, no two adjacent dependencies can be as -(*R)-> -(S*)->.
Now our mission is to make __bfs() traverse only the strong dependency
paths, which is simple: we record whether we only have -(*R)-> for the
previous lock_list of the path in lock_list::only_xr, and when we pick a
dependency in the traverse, we 1) filter out -(S*)-> dependency if the
previous lock_list only has -(*R)-> dependency (i.e. ->only_xr is true)
and 2) set the next lock_list::only_xr to true if we only have -(*R)->
left after we filter out dependencies based on 1), otherwise, set it to
false.
With this extension for __bfs(), we now need to initialize the root of
__bfs() properly (with a correct ->only_xr), to do so, we introduce some
helper functions, which also cleans up a little bit for the __bfs() root
initialization code.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-8-boqun.feng@gmail.com
To add recursive read locks into the dependency graph, we need to store
the types of dependencies for the BFS later. There are four types of
dependencies:
* Exclusive -> Non-recursive dependencies: EN
e.g. write_lock(prev) held and try to acquire write_lock(next)
or non-recursive read_lock(next), which can be represented as
"prev -(EN)-> next"
* Shared -> Non-recursive dependencies: SN
e.g. read_lock(prev) held and try to acquire write_lock(next) or
non-recursive read_lock(next), which can be represented as
"prev -(SN)-> next"
* Exclusive -> Recursive dependencies: ER
e.g. write_lock(prev) held and try to acquire recursive
read_lock(next), which can be represented as "prev -(ER)-> next"
* Shared -> Recursive dependencies: SR
e.g. read_lock(prev) held and try to acquire recursive
read_lock(next), which can be represented as "prev -(SR)-> next"
So we use 4 bits for the presence of each type in lock_list::dep. Helper
functions and macros are also introduced to convert a pair of locks into
lock_list::dep bit and maintain the addition of different types of
dependencies.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-7-boqun.feng@gmail.com
lock_list::distance is always not greater than MAX_LOCK_DEPTH (which
is 48 right now), so a u16 will fit. This patch reduces the size of
lock_list::distance to save space, so that we can introduce other fields
to help detect recursive read lock deadlocks without increasing the size
of lock_list structure.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-6-boqun.feng@gmail.com
Currently, __bfs() will do a breadth-first search in the dependency
graph and visit each lock class in the graph exactly once, so for
example, in the following graph:
A ---------> B
| ^
| |
+----------> C
a __bfs() call starts at A, will visit B through dependency A -> B and
visit C through dependency A -> C and that's it, IOW, __bfs() will not
visit dependency C -> B.
This is OK for now, as we only have strong dependencies in the
dependency graph, so whenever there is a traverse path from A to B in
__bfs(), it means A has strong dependencies to B (IOW, B depends on A
strongly). So no need to visit all dependencies in the graph.
However, as we are going to add recursive-read lock into the dependency
graph, as a result, not all the paths mean strong dependencies, in the
same example above, dependency A -> B may be a weak dependency and
traverse A -> C -> B may be a strong dependency path. And with the old
way of __bfs() (i.e. visiting every lock class exactly once), we will
miss the strong dependency path, which will result into failing to find
a deadlock. To cure this for the future, we need to find a way for
__bfs() to visit each dependency, rather than each class, exactly once
in the search until we find a match.
The solution is simple:
We used to mark lock_class::lockdep_dependency_gen_id to indicate a
class has been visited in __bfs(), now we change the semantics a little
bit: we now mark lock_class::lockdep_dependency_gen_id to indicate _all
the dependencies_ in its lock_{after,before} have been visited in the
__bfs() (note we only take one direction in a __bfs() search). In this
way, every dependency is guaranteed to be visited until we find a match.
Note: the checks in mark_lock_accessed() and lock_accessed() are
removed, because after this modification, we may call these two
functions on @source_entry of __bfs(), which may not be the entry in
"list_entries"
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-5-boqun.feng@gmail.com
__bfs() could return four magic numbers:
1: search succeeds, but none match.
0: search succeeds, find one match.
-1: search fails because of the cq is full.
-2: search fails because a invalid node is found.
This patch cleans things up by using a enum type for the return value
of __bfs() and its friends, this improves the code readability of the
code, and further, could help if we want to extend the BFS.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-4-boqun.feng@gmail.com
On the archs using QUEUED_RWLOCKS, read_lock() is not always a recursive
read lock, actually it's only recursive if in_interrupt() is true. So
change the annotation accordingly to catch more deadlocks.
Note we used to treat read_lock() as pure recursive read locks in
lib/locking-seftest.c, and this is useful, especially for the lockdep
development selftest, so we keep this via a variable to force switching
lock annotation for read_lock().
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-2-boqun.feng@gmail.com
The lockdep tracepoints are under the lockdep recursion counter, this
has a bunch of nasty side effects:
- TRACE_IRQFLAGS doesn't work across the entire tracepoint
- RCU-lockdep doesn't see the tracepoints either, hiding numerous
"suspicious RCU usage" warnings.
Pull the trace_lock_*() tracepoints completely out from under the
lockdep recursion handling and completely rely on the trace level
recusion handling -- also, tracing *SHOULD* not be taking locks in any
case.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Marco Elver <elver@google.com>
Link: https://lkml.kernel.org/r/20200821085348.782688941@infradead.org
Sven reported that commit a21ee6055c ("lockdep: Change
hardirq{s_enabled,_context} to per-cpu variables") caused trouble on
s390 because their this_cpu_*() primitives disable preemption which
then lands back tracing.
On the one hand, per-cpu ops should use preempt_*able_notrace() and
raw_local_irq_*(), on the other hand, we can trivialy use raw_cpu_*()
ops for this.
Fixes: a21ee6055c ("lockdep: Change hardirq{s_enabled,_context} to per-cpu variables")
Reported-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200821085348.192346882@infradead.org
The sparse tool complains as follows:
kernel/locking/locktorture.c:569:6: warning:
symbol 'torture_percpu_rwsem_init' was not declared. Should it be static?
And this function is not used outside of locktorture.c,
so this commit marks it static.
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
- Untangle the header spaghetti which causes build failures in various
situations caused by the lockdep additions to seqcount to validate that
the write side critical sections are non-preemptible.
- The seqcount associated lock debug addons which were blocked by the
above fallout.
seqcount writers contrary to seqlock writers must be externally
serialized, which usually happens via locking - except for strict per
CPU seqcounts. As the lock is not part of the seqcount, lockdep cannot
validate that the lock is held.
This new debug mechanism adds the concept of associated locks.
sequence count has now lock type variants and corresponding
initializers which take a pointer to the associated lock used for
writer serialization. If lockdep is enabled the pointer is stored and
write_seqcount_begin() has a lockdep assertion to validate that the
lock is held.
Aside of the type and the initializer no other code changes are
required at the seqcount usage sites. The rest of the seqcount API is
unchanged and determines the type at compile time with the help of
_Generic which is possible now that the minimal GCC version has been
moved up.
Adding this lockdep coverage unearthed a handful of seqcount bugs which
have been addressed already independent of this.
While generaly useful this comes with a Trojan Horse twist: On RT
kernels the write side critical section can become preemtible if the
writers are serialized by an associated lock, which leads to the well
known reader preempts writer livelock. RT prevents this by storing the
associated lock pointer independent of lockdep in the seqcount and
changing the reader side to block on the lock when a reader detects
that a writer is in the write side critical section.
- Conversion of seqcount usage sites to associated types and initializers.
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Merge tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Thomas Gleixner:
"A set of locking fixes and updates:
- Untangle the header spaghetti which causes build failures in
various situations caused by the lockdep additions to seqcount to
validate that the write side critical sections are non-preemptible.
- The seqcount associated lock debug addons which were blocked by the
above fallout.
seqcount writers contrary to seqlock writers must be externally
serialized, which usually happens via locking - except for strict
per CPU seqcounts. As the lock is not part of the seqcount, lockdep
cannot validate that the lock is held.
This new debug mechanism adds the concept of associated locks.
sequence count has now lock type variants and corresponding
initializers which take a pointer to the associated lock used for
writer serialization. If lockdep is enabled the pointer is stored
and write_seqcount_begin() has a lockdep assertion to validate that
the lock is held.
Aside of the type and the initializer no other code changes are
required at the seqcount usage sites. The rest of the seqcount API
is unchanged and determines the type at compile time with the help
of _Generic which is possible now that the minimal GCC version has
been moved up.
Adding this lockdep coverage unearthed a handful of seqcount bugs
which have been addressed already independent of this.
While generally useful this comes with a Trojan Horse twist: On RT
kernels the write side critical section can become preemtible if
the writers are serialized by an associated lock, which leads to
the well known reader preempts writer livelock. RT prevents this by
storing the associated lock pointer independent of lockdep in the
seqcount and changing the reader side to block on the lock when a
reader detects that a writer is in the write side critical section.
- Conversion of seqcount usage sites to associated types and
initializers"
* tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (25 commits)
locking/seqlock, headers: Untangle the spaghetti monster
locking, arch/ia64: Reduce <asm/smp.h> header dependencies by moving XTP bits into the new <asm/xtp.h> header
x86/headers: Remove APIC headers from <asm/smp.h>
seqcount: More consistent seqprop names
seqcount: Compress SEQCNT_LOCKNAME_ZERO()
seqlock: Fold seqcount_LOCKNAME_init() definition
seqlock: Fold seqcount_LOCKNAME_t definition
seqlock: s/__SEQ_LOCKDEP/__SEQ_LOCK/g
hrtimer: Use sequence counter with associated raw spinlock
kvm/eventfd: Use sequence counter with associated spinlock
userfaultfd: Use sequence counter with associated spinlock
NFSv4: Use sequence counter with associated spinlock
iocost: Use sequence counter with associated spinlock
raid5: Use sequence counter with associated spinlock
vfs: Use sequence counter with associated spinlock
timekeeping: Use sequence counter with associated raw spinlock
xfrm: policy: Use sequence counters with associated lock
netfilter: nft_set_rbtree: Use sequence counter with associated rwlock
netfilter: conntrack: Use sequence counter with associated spinlock
sched: tasks: Use sequence counter with associated spinlock
...
x86:
* Report last CPU for debugging
* Emulate smaller MAXPHYADDR in the guest than in the host
* .noinstr and tracing fixes from Thomas
* nested SVM page table switching optimization and fixes
Generic:
* Unify shadow MMU cache data structures across architectures
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Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm
Pull KVM updates from Paolo Bonzini:
"s390:
- implement diag318
x86:
- Report last CPU for debugging
- Emulate smaller MAXPHYADDR in the guest than in the host
- .noinstr and tracing fixes from Thomas
- nested SVM page table switching optimization and fixes
Generic:
- Unify shadow MMU cache data structures across architectures"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (127 commits)
KVM: SVM: Fix sev_pin_memory() error handling
KVM: LAPIC: Set the TDCR settable bits
KVM: x86: Specify max TDP level via kvm_configure_mmu()
KVM: x86/mmu: Rename max_page_level to max_huge_page_level
KVM: x86: Dynamically calculate TDP level from max level and MAXPHYADDR
KVM: VXM: Remove temporary WARN on expected vs. actual EPTP level mismatch
KVM: x86: Pull the PGD's level from the MMU instead of recalculating it
KVM: VMX: Make vmx_load_mmu_pgd() static
KVM: x86/mmu: Add separate helper for shadow NPT root page role calc
KVM: VMX: Drop a duplicate declaration of construct_eptp()
KVM: nSVM: Correctly set the shadow NPT root level in its MMU role
KVM: Using macros instead of magic values
MIPS: KVM: Fix build error caused by 'kvm_run' cleanup
KVM: nSVM: remove nonsensical EXITINFO1 adjustment on nested NPF
KVM: x86: Add a capability for GUEST_MAXPHYADDR < HOST_MAXPHYADDR support
KVM: VMX: optimize #PF injection when MAXPHYADDR does not match
KVM: VMX: Add guest physical address check in EPT violation and misconfig
KVM: VMX: introduce vmx_need_pf_intercept
KVM: x86: update exception bitmap on CPUID changes
KVM: x86: rename update_bp_intercept to update_exception_bitmap
...
static priority level knowledge from non-scheduler code.
The three APIs for non-scheduler code to set SCHED_FIFO are:
- sched_set_fifo()
- sched_set_fifo_low()
- sched_set_normal()
These are two FIFO priority levels: default (high), and a 'low' priority level,
plus sched_set_normal() to set the policy back to non-SCHED_FIFO.
Since the changes affect a lot of non-scheduler code, we kept this in a separate
tree.
When merging to the latest upstream tree there's a conflict in drivers/spi/spi.c,
which can be resolved via:
sched_set_fifo(ctlr->kworker_task);
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-fifo-2020-08-04' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull sched/fifo updates from Ingo Molnar:
"This adds the sched_set_fifo*() encapsulation APIs to remove static
priority level knowledge from non-scheduler code.
The three APIs for non-scheduler code to set SCHED_FIFO are:
- sched_set_fifo()
- sched_set_fifo_low()
- sched_set_normal()
These are two FIFO priority levels: default (high), and a 'low'
priority level, plus sched_set_normal() to set the policy back to
non-SCHED_FIFO.
Since the changes affect a lot of non-scheduler code, we kept this in
a separate tree"
* tag 'sched-fifo-2020-08-04' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits)
sched,tracing: Convert to sched_set_fifo()
sched: Remove sched_set_*() return value
sched: Remove sched_setscheduler*() EXPORTs
sched,psi: Convert to sched_set_fifo_low()
sched,rcutorture: Convert to sched_set_fifo_low()
sched,rcuperf: Convert to sched_set_fifo_low()
sched,locktorture: Convert to sched_set_fifo()
sched,irq: Convert to sched_set_fifo()
sched,watchdog: Convert to sched_set_fifo()
sched,serial: Convert to sched_set_fifo()
sched,powerclamp: Convert to sched_set_fifo()
sched,ion: Convert to sched_set_normal()
sched,powercap: Convert to sched_set_fifo*()
sched,spi: Convert to sched_set_fifo*()
sched,mmc: Convert to sched_set_fifo*()
sched,ivtv: Convert to sched_set_fifo*()
sched,drm/scheduler: Convert to sched_set_fifo*()
sched,msm: Convert to sched_set_fifo*()
sched,psci: Convert to sched_set_fifo*()
sched,drbd: Convert to sched_set_fifo*()
...
- LKMM updates: mostly documentation changes, but also some new litmus tests for atomic ops.
- KCSAN updates: the most important change is that GCC 11 now has all fixes in place
to support KCSAN, so GCC support can be enabled again. Also more annotations.
- futex updates: minor cleanups and simplifications
- seqlock updates: merge preparatory changes/cleanups for the 'associated locks' facilities.
- lockdep updates:
- simplify IRQ trace event handling
- add various new debug checks
- simplify header dependencies, split out <linux/lockdep_types.h>, decouple
lockdep from other low level headers some more
- fix NMI handling
- misc cleanups and smaller fixes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'locking-core-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
- LKMM updates: mostly documentation changes, but also some new litmus
tests for atomic ops.
- KCSAN updates: the most important change is that GCC 11 now has all
fixes in place to support KCSAN, so GCC support can be enabled again.
Also more annotations.
- futex updates: minor cleanups and simplifications
- seqlock updates: merge preparatory changes/cleanups for the
'associated locks' facilities.
- lockdep updates:
- simplify IRQ trace event handling
- add various new debug checks
- simplify header dependencies, split out <linux/lockdep_types.h>,
decouple lockdep from other low level headers some more
- fix NMI handling
- misc cleanups and smaller fixes
* tag 'locking-core-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (60 commits)
kcsan: Improve IRQ state trace reporting
lockdep: Refactor IRQ trace events fields into struct
seqlock: lockdep assert non-preemptibility on seqcount_t write
lockdep: Add preemption enabled/disabled assertion APIs
seqlock: Implement raw_seqcount_begin() in terms of raw_read_seqcount()
seqlock: Add kernel-doc for seqcount_t and seqlock_t APIs
seqlock: Reorder seqcount_t and seqlock_t API definitions
seqlock: seqcount_t latch: End read sections with read_seqcount_retry()
seqlock: Properly format kernel-doc code samples
Documentation: locking: Describe seqlock design and usage
locking/qspinlock: Do not include atomic.h from qspinlock_types.h
locking/atomic: Move ATOMIC_INIT into linux/types.h
lockdep: Move list.h inclusion into lockdep.h
locking/lockdep: Fix TRACE_IRQFLAGS vs. NMIs
futex: Remove unused or redundant includes
futex: Consistently use fshared as boolean
futex: Remove needless goto's
futex: Remove put_futex_key()
rwsem: fix commas in initialisation
docs: locking: Replace HTTP links with HTTPS ones
...
Pull v5.9 KCSAN bits from Paul E. McKenney.
Perhaps the most important change is that GCC 11 now has all fixes in place
to support KCSAN, so GCC support can be enabled again.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Refactor the IRQ trace events fields, used for printing information
about the IRQ trace events, into a separate struct 'irqtrace_events'.
This improves readability by separating the information only used in
reporting, as well as enables (simplified) storing/restoring of
irqtrace_events snapshots.
No functional change intended.
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200729110916.3920464-1-elver@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Prior to commit:
859d069ee1 ("lockdep: Prepare for NMI IRQ state tracking")
IRQ state tracking was disabled in NMIs due to nmi_enter()
doing lockdep_off() -- with the obvious requirement that NMI entry
call nmi_enter() before trace_hardirqs_off().
[ AFAICT, PowerPC and SH violate this order on their NMI entry ]
However, that commit explicitly changed lockdep_hardirqs_*() to ignore
lockdep_off() and breaks every architecture that has irq-tracing in
it's NMI entry that hasn't been fixed up (x86 being the only fixed one
at this point).
The reason for this change is that by ignoring lockdep_off() we can:
- get rid of 'current->lockdep_recursion' in lockdep_assert_irqs*()
which was going to to give header-recursion issues with the
seqlock rework.
- allow these lockdep_assert_*() macros to function in NMI context.
Restore the previous state of things and allow an architecture to
opt-in to the NMI IRQ tracking support, however instead of relying on
lockdep_off(), rely on in_nmi(), both are part of nmi_enter() and so
over-all entry ordering doesn't need to change.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200727124852.GK119549@hirez.programming.kicks-ass.net
Though the number of lock-acquisitions is tracked as unsigned long, this
is passed as the divisor to div_s64() which interprets it as a s32,
giving nonsense values with more than 2 billion acquisitons. E.g.
acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg
-------------------------------------------------------------------------
2350439395 0.07 353.38 649647067.36 0.-32
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200725185110.11588-1-chris@chris-wilson.co.uk
Using uninitialized_var() is dangerous as it papers over real bugs[1]
(or can in the future), and suppresses unrelated compiler warnings
(e.g. "unused variable"). If the compiler thinks it is uninitialized,
either simply initialize the variable or make compiler changes.
In preparation for removing[2] the[3] macro[4], remove all remaining
needless uses with the following script:
git grep '\buninitialized_var\b' | cut -d: -f1 | sort -u | \
xargs perl -pi -e \
's/\buninitialized_var\(([^\)]+)\)/\1/g;
s:\s*/\* (GCC be quiet|to make compiler happy) \*/$::g;'
drivers/video/fbdev/riva/riva_hw.c was manually tweaked to avoid
pathological white-space.
No outstanding warnings were found building allmodconfig with GCC 9.3.0
for x86_64, i386, arm64, arm, powerpc, powerpc64le, s390x, mips, sparc64,
alpha, and m68k.
[1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
[2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
[3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
[4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
Reviewed-by: Leon Romanovsky <leonro@mellanox.com> # drivers/infiniband and mlx4/mlx5
Acked-by: Jason Gunthorpe <jgg@mellanox.com> # IB
Acked-by: Kalle Valo <kvalo@codeaurora.org> # wireless drivers
Reviewed-by: Chao Yu <yuchao0@huawei.com> # erofs
Signed-off-by: Kees Cook <keescook@chromium.org>
Currently all IRQ-tracking state is in task_struct, this means that
task_struct needs to be defined before we use it.
Especially for lockdep_assert_irq*() this can lead to header-hell.
Move the hardirq state into per-cpu variables to avoid the task_struct
dependency.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200623083721.512673481@infradead.org
There is no reason not to always, accurately, track IRQ state.
This change also makes IRQ state tracking ignore lockdep_off().
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200623083721.155449112@infradead.org
There are cases where a guest tries to switch spinlocks to bare metal
behavior (e.g. by setting "xen_nopvspin" on XEN platform and
"hv_nopvspin" on HYPER_V).
That feature is missed on KVM, add a new parameter "nopvspin" to disable
PV spinlocks for KVM guest.
The new 'nopvspin' parameter will also replace Xen and Hyper-V specific
parameters in future patches.
Define variable nopvsin as global because it will be used in future
patches as above.
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krcmar <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The prev->next pointer can be accessed concurrently as noticed by KCSAN:
write (marked) to 0xffff9d3370dbbe40 of 8 bytes by task 3294 on cpu 107:
osq_lock+0x25f/0x350
osq_wait_next at kernel/locking/osq_lock.c:79
(inlined by) osq_lock at kernel/locking/osq_lock.c:185
rwsem_optimistic_spin
<snip>
read to 0xffff9d3370dbbe40 of 8 bytes by task 3398 on cpu 100:
osq_lock+0x196/0x350
osq_lock at kernel/locking/osq_lock.c:157
rwsem_optimistic_spin
<snip>
Since the write only stores NULL to prev->next and the read tests if
prev->next equals to this_cpu_ptr(&osq_node). Even if the value is
shattered, the code is still working correctly. Thus, mark it as an
intentional data race using the data_race() macro.
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit fixes the following coccicheck warnings:
kernel/locking/locktorture.c:689:6-10: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:907:2-20: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:938:3-20: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:668:2-19: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:674:2-19: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:634:2-20: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:640:2-20: WARNING: Assignment of 0/1 to bool variable
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, lockdep_rcu_suspicious() complains twice about RCU read-side
critical sections being invoked from within extended quiescent states,
for example:
RCU used illegally from idle CPU!
rcu_scheduler_active = 2, debug_locks = 1
RCU used illegally from extended quiescent state!
This commit therefore saves a couple lines of code and one line of
console-log output by eliminating the first of these two complaints.
Link: https://lore.kernel.org/lkml/87wo4wnpzb.fsf@nanos.tec.linutronix.de
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Because SCHED_FIFO is a broken scheduler model (see previous patches)
take away the priority field, the kernel can't possibly make an
informed decision.
Effectively changes prio from 99 to 50.
Cc: paulmck@kernel.org
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
This all started about 6 month ago with the attempt to move the Posix CPU
timer heavy lifting out of the timer interrupt code and just have lockless
quick checks in that code path. Trivial 5 patches.
This unearthed an inconsistency in the KVM handling of task work and the
review requested to move all of this into generic code so other
architectures can share.
Valid request and solved with another 25 patches but those unearthed
inconsistencies vs. RCU and instrumentation.
Digging into this made it obvious that there are quite some inconsistencies
vs. instrumentation in general. The int3 text poke handling in particular
was completely unprotected and with the batched update of trace events even
more likely to expose to endless int3 recursion.
In parallel the RCU implications of instrumenting fragile entry code came
up in several discussions.
The conclusion of the X86 maintainer team was to go all the way and make
the protection against any form of instrumentation of fragile and dangerous
code pathes enforcable and verifiable by tooling.
A first batch of preparatory work hit mainline with commit d5f744f9a2.
The (almost) full solution introduced a new code section '.noinstr.text'
into which all code which needs to be protected from instrumentation of all
sorts goes into. Any call into instrumentable code out of this section has
to be annotated. objtool has support to validate this. Kprobes now excludes
this section fully which also prevents BPF from fiddling with it and all
'noinstr' annotated functions also keep ftrace off. The section, kprobes
and objtool changes are already merged.
The major changes coming with this are:
- Preparatory cleanups
- Annotating of relevant functions to move them into the noinstr.text
section or enforcing inlining by marking them __always_inline so the
compiler cannot misplace or instrument them.
- Splitting and simplifying the idtentry macro maze so that it is now
clearly separated into simple exception entries and the more
interesting ones which use interrupt stacks and have the paranoid
handling vs. CR3 and GS.
- Move quite some of the low level ASM functionality into C code:
- enter_from and exit to user space handling. The ASM code now calls
into C after doing the really necessary ASM handling and the return
path goes back out without bells and whistels in ASM.
- exception entry/exit got the equivivalent treatment
- move all IRQ tracepoints from ASM to C so they can be placed as
appropriate which is especially important for the int3 recursion
issue.
- Consolidate the declaration and definition of entry points between 32
and 64 bit. They share a common header and macros now.
- Remove the extra device interrupt entry maze and just use the regular
exception entry code.
- All ASM entry points except NMI are now generated from the shared header
file and the corresponding macros in the 32 and 64 bit entry ASM.
- The C code entry points are consolidated as well with the help of
DEFINE_IDTENTRY*() macros. This allows to ensure at one central point
that all corresponding entry points share the same semantics. The
actual function body for most entry points is in an instrumentable
and sane state.
There are special macros for the more sensitive entry points,
e.g. INT3 and of course the nasty paranoid #NMI, #MCE, #DB and #DF.
They allow to put the whole entry instrumentation and RCU handling
into safe places instead of the previous pray that it is correct
approach.
- The INT3 text poke handling is now completely isolated and the
recursion issue banned. Aside of the entry rework this required other
isolation work, e.g. the ability to force inline bsearch.
- Prevent #DB on fragile entry code, entry relevant memory and disable
it on NMI, #MC entry, which allowed to get rid of the nested #DB IST
stack shifting hackery.
- A few other cleanups and enhancements which have been made possible
through this and already merged changes, e.g. consolidating and
further restricting the IDT code so the IDT table becomes RO after
init which removes yet another popular attack vector
- About 680 lines of ASM maze are gone.
There are a few open issues:
- An escape out of the noinstr section in the MCE handler which needs
some more thought but under the aspect that MCE is a complete
trainwreck by design and the propability to survive it is low, this was
not high on the priority list.
- Paravirtualization
When PV is enabled then objtool complains about a bunch of indirect
calls out of the noinstr section. There are a few straight forward
ways to fix this, but the other issues vs. general correctness were
more pressing than parawitz.
- KVM
KVM is inconsistent as well. Patches have been posted, but they have
not yet been commented on or picked up by the KVM folks.
- IDLE
Pretty much the same problems can be found in the low level idle code
especially the parts where RCU stopped watching. This was beyond the
scope of the more obvious and exposable problems and is on the todo
list.
The lesson learned from this brain melting exercise to morph the evolved
code base into something which can be validated and understood is that once
again the violation of the most important engineering principle
"correctness first" has caused quite a few people to spend valuable time on
problems which could have been avoided in the first place. The "features
first" tinkering mindset really has to stop.
With that I want to say thanks to everyone involved in contributing to this
effort. Special thanks go to the following people (alphabetical order):
Alexandre Chartre
Andy Lutomirski
Borislav Petkov
Brian Gerst
Frederic Weisbecker
Josh Poimboeuf
Juergen Gross
Lai Jiangshan
Macro Elver
Paolo Bonzini
Paul McKenney
Peter Zijlstra
Vitaly Kuznetsov
Will Deacon
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Merge tag 'x86-entry-2020-06-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 entry updates from Thomas Gleixner:
"The x86 entry, exception and interrupt code rework
This all started about 6 month ago with the attempt to move the Posix
CPU timer heavy lifting out of the timer interrupt code and just have
lockless quick checks in that code path. Trivial 5 patches.
This unearthed an inconsistency in the KVM handling of task work and
the review requested to move all of this into generic code so other
architectures can share.
Valid request and solved with another 25 patches but those unearthed
inconsistencies vs. RCU and instrumentation.
Digging into this made it obvious that there are quite some
inconsistencies vs. instrumentation in general. The int3 text poke
handling in particular was completely unprotected and with the batched
update of trace events even more likely to expose to endless int3
recursion.
In parallel the RCU implications of instrumenting fragile entry code
came up in several discussions.
The conclusion of the x86 maintainer team was to go all the way and
make the protection against any form of instrumentation of fragile and
dangerous code pathes enforcable and verifiable by tooling.
A first batch of preparatory work hit mainline with commit
d5f744f9a2 ("Pull x86 entry code updates from Thomas Gleixner")
That (almost) full solution introduced a new code section
'.noinstr.text' into which all code which needs to be protected from
instrumentation of all sorts goes into. Any call into instrumentable
code out of this section has to be annotated. objtool has support to
validate this.
Kprobes now excludes this section fully which also prevents BPF from
fiddling with it and all 'noinstr' annotated functions also keep
ftrace off. The section, kprobes and objtool changes are already
merged.
The major changes coming with this are:
- Preparatory cleanups
- Annotating of relevant functions to move them into the
noinstr.text section or enforcing inlining by marking them
__always_inline so the compiler cannot misplace or instrument
them.
- Splitting and simplifying the idtentry macro maze so that it is
now clearly separated into simple exception entries and the more
interesting ones which use interrupt stacks and have the paranoid
handling vs. CR3 and GS.
- Move quite some of the low level ASM functionality into C code:
- enter_from and exit to user space handling. The ASM code now
calls into C after doing the really necessary ASM handling and
the return path goes back out without bells and whistels in
ASM.
- exception entry/exit got the equivivalent treatment
- move all IRQ tracepoints from ASM to C so they can be placed as
appropriate which is especially important for the int3
recursion issue.
- Consolidate the declaration and definition of entry points between
32 and 64 bit. They share a common header and macros now.
- Remove the extra device interrupt entry maze and just use the
regular exception entry code.
- All ASM entry points except NMI are now generated from the shared
header file and the corresponding macros in the 32 and 64 bit
entry ASM.
- The C code entry points are consolidated as well with the help of
DEFINE_IDTENTRY*() macros. This allows to ensure at one central
point that all corresponding entry points share the same
semantics. The actual function body for most entry points is in an
instrumentable and sane state.
There are special macros for the more sensitive entry points, e.g.
INT3 and of course the nasty paranoid #NMI, #MCE, #DB and #DF.
They allow to put the whole entry instrumentation and RCU handling
into safe places instead of the previous pray that it is correct
approach.
- The INT3 text poke handling is now completely isolated and the
recursion issue banned. Aside of the entry rework this required
other isolation work, e.g. the ability to force inline bsearch.
- Prevent #DB on fragile entry code, entry relevant memory and
disable it on NMI, #MC entry, which allowed to get rid of the
nested #DB IST stack shifting hackery.
- A few other cleanups and enhancements which have been made
possible through this and already merged changes, e.g.
consolidating and further restricting the IDT code so the IDT
table becomes RO after init which removes yet another popular
attack vector
- About 680 lines of ASM maze are gone.
There are a few open issues:
- An escape out of the noinstr section in the MCE handler which needs
some more thought but under the aspect that MCE is a complete
trainwreck by design and the propability to survive it is low, this
was not high on the priority list.
- Paravirtualization
When PV is enabled then objtool complains about a bunch of indirect
calls out of the noinstr section. There are a few straight forward
ways to fix this, but the other issues vs. general correctness were
more pressing than parawitz.
- KVM
KVM is inconsistent as well. Patches have been posted, but they
have not yet been commented on or picked up by the KVM folks.
- IDLE
Pretty much the same problems can be found in the low level idle
code especially the parts where RCU stopped watching. This was
beyond the scope of the more obvious and exposable problems and is
on the todo list.
The lesson learned from this brain melting exercise to morph the
evolved code base into something which can be validated and understood
is that once again the violation of the most important engineering
principle "correctness first" has caused quite a few people to spend
valuable time on problems which could have been avoided in the first
place. The "features first" tinkering mindset really has to stop.
With that I want to say thanks to everyone involved in contributing to
this effort. Special thanks go to the following people (alphabetical
order): Alexandre Chartre, Andy Lutomirski, Borislav Petkov, Brian
Gerst, Frederic Weisbecker, Josh Poimboeuf, Juergen Gross, Lai
Jiangshan, Macro Elver, Paolo Bonzin,i Paul McKenney, Peter Zijlstra,
Vitaly Kuznetsov, and Will Deacon"
* tag 'x86-entry-2020-06-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (142 commits)
x86/entry: Force rcu_irq_enter() when in idle task
x86/entry: Make NMI use IDTENTRY_RAW
x86/entry: Treat BUG/WARN as NMI-like entries
x86/entry: Unbreak __irqentry_text_start/end magic
x86/entry: __always_inline CR2 for noinstr
lockdep: __always_inline more for noinstr
x86/entry: Re-order #DB handler to avoid *SAN instrumentation
x86/entry: __always_inline arch_atomic_* for noinstr
x86/entry: __always_inline irqflags for noinstr
x86/entry: __always_inline debugreg for noinstr
x86/idt: Consolidate idt functionality
x86/idt: Cleanup trap_init()
x86/idt: Use proper constants for table size
x86/idt: Add comments about early #PF handling
x86/idt: Mark init only functions __init
x86/entry: Rename trace_hardirqs_off_prepare()
x86/entry: Clarify irq_{enter,exit}_rcu()
x86/entry: Remove DBn stacks
x86/entry: Remove debug IDT frobbing
x86/entry: Optimize local_db_save() for virt
...
Merge the state of the locking kcsan branch before the read/write_once()
and the atomics modifications got merged.
Squash the fallout of the rebase on top of the read/write once and atomic
fallback work into the merge. The history of the original branch is
preserved in tag locking-kcsan-2020-06-02.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Now the last users of show_stack() got converted to use an explicit log
level, show_stack_loglvl() can drop it's redundant suffix and become once
again well known show_stack().
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200418201944.482088-51-dima@arista.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Align the last users of show_stack() by KERN_DEFAULT as the surrounding
headers/messages.
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Link: http://lkml.kernel.org/r/20200418201944.482088-50-dima@arista.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Patch series "Add log level to show_stack()", v3.
Add log level argument to show_stack().
Done in three stages:
1. Introducing show_stack_loglvl() for every architecture
2. Migrating old users with an explicit log level
3. Renaming show_stack_loglvl() into show_stack()
Justification:
- It's a design mistake to move a business-logic decision into platform
realization detail.
- I have currently two patches sets that would benefit from this work:
Removing console_loglevel jumps in sysrq driver [1] Hung task warning
before panic [2] - suggested by Tetsuo (but he probably didn't realise
what it would involve).
- While doing (1), (2) the backtraces were adjusted to headers and other
messages for each situation - so there won't be a situation when the
backtrace is printed, but the headers are missing because they have
lesser log level (or the reverse).
- As the result in (2) plays with console_loglevel for kdb are removed.
The least important for upstream, but maybe still worth to note that every
company I've worked in so far had an off-list patch to print backtrace
with the needed log level (but only for the architecture they cared
about). If you have other ideas how you will benefit from show_stack()
with a log level - please, reply to this cover letter.
See also discussion on v1:
https://lore.kernel.org/linux-riscv/20191106083538.z5nlpuf64cigxigh@pathway.suse.cz/
This patch (of 50):
print_ip_sym() needs to have a log level parameter to comply with other
parts being printed. Otherwise, half of the expected backtrace would be
printed and other may be missing with some logging level.
The following callee(s) are using now the adjusted log level:
- microblaze/unwind: the same level as headers & userspace unwind.
Note that pr_debug()'s there are for debugging the unwinder itself.
- nds32/traps: symbol addresses are printed with the same log level
as backtrace headers.
- lockdep: ip for locking issues is printed with the same log level
as other part of the warning.
- sched: ip where preemption was disabled is printed as error like
the rest part of the message.
- ftrace: bug reports are now consistent in the log level being used.
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Ben Segall <bsegall@google.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Greentime Hu <green.hu@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Chen <deanbo422@gmail.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Will Deacon <will@kernel.org>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Dmitry Safonov <dima@arista.com>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Aurelien Jacquiot <jacquiot.aurelien@gmail.com>
Cc: Mark Salter <msalter@redhat.com>
Cc: Guo Ren <guoren@kernel.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Brian Cain <bcain@codeaurora.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Ley Foon Tan <lftan@altera.com>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Helge Deller <deller@gmx.de>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Rich Felker <dalias@libc.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Guan Xuetao <gxt@pku.edu.cn>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Jason Wessel <jason.wessel@windriver.com>
Link: http://lkml.kernel.org/r/20200418201944.482088-2-dima@arista.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
- Move the arch-specific code into arch/arm64/kvm
- Start the post-32bit cleanup
- Cherry-pick a few non-invasive pre-NV patches
x86:
- Rework of TLB flushing
- Rework of event injection, especially with respect to nested virtualization
- Nested AMD event injection facelift, building on the rework of generic code
and fixing a lot of corner cases
- Nested AMD live migration support
- Optimization for TSC deadline MSR writes and IPIs
- Various cleanups
- Asynchronous page fault cleanups (from tglx, common topic branch with tip tree)
- Interrupt-based delivery of asynchronous "page ready" events (host side)
- Hyper-V MSRs and hypercalls for guest debugging
- VMX preemption timer fixes
s390:
- Cleanups
Generic:
- switch vCPU thread wakeup from swait to rcuwait
The other architectures, and the guest side of the asynchronous page fault
work, will come next week.
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Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm
Pull kvm updates from Paolo Bonzini:
"ARM:
- Move the arch-specific code into arch/arm64/kvm
- Start the post-32bit cleanup
- Cherry-pick a few non-invasive pre-NV patches
x86:
- Rework of TLB flushing
- Rework of event injection, especially with respect to nested
virtualization
- Nested AMD event injection facelift, building on the rework of
generic code and fixing a lot of corner cases
- Nested AMD live migration support
- Optimization for TSC deadline MSR writes and IPIs
- Various cleanups
- Asynchronous page fault cleanups (from tglx, common topic branch
with tip tree)
- Interrupt-based delivery of asynchronous "page ready" events (host
side)
- Hyper-V MSRs and hypercalls for guest debugging
- VMX preemption timer fixes
s390:
- Cleanups
Generic:
- switch vCPU thread wakeup from swait to rcuwait
The other architectures, and the guest side of the asynchronous page
fault work, will come next week"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (256 commits)
KVM: selftests: fix rdtsc() for vmx_tsc_adjust_test
KVM: check userspace_addr for all memslots
KVM: selftests: update hyperv_cpuid with SynDBG tests
x86/kvm/hyper-v: Add support for synthetic debugger via hypercalls
x86/kvm/hyper-v: enable hypercalls regardless of hypercall page
x86/kvm/hyper-v: Add support for synthetic debugger interface
x86/hyper-v: Add synthetic debugger definitions
KVM: selftests: VMX preemption timer migration test
KVM: nVMX: Fix VMX preemption timer migration
x86/kvm/hyper-v: Explicitly align hcall param for kvm_hyperv_exit
KVM: x86/pmu: Support full width counting
KVM: x86/pmu: Tweak kvm_pmu_get_msr to pass 'struct msr_data' in
KVM: x86: announce KVM_FEATURE_ASYNC_PF_INT
KVM: x86: acknowledgment mechanism for async pf page ready notifications
KVM: x86: interrupt based APF 'page ready' event delivery
KVM: introduce kvm_read_guest_offset_cached()
KVM: rename kvm_arch_can_inject_async_page_present() to kvm_arch_can_dequeue_async_page_present()
KVM: x86: extend struct kvm_vcpu_pv_apf_data with token info
Revert "KVM: async_pf: Fix #DF due to inject "Page not Present" and "Page Ready" exceptions simultaneously"
KVM: VMX: Replace zero-length array with flexible-array
...
of local_lock_t - this primitive comes from the -rt project and identifies
CPU-local locking dependencies normally handled opaquely beind preempt_disable()
or local_irq_save/disable() critical sections.
The generated code on mainline kernels doesn't change as a result, but still there
are benefits: improved debugging and better documentation of data structure
accesses.
The new local_lock_t primitives are introduced and then utilized in a couple of
kernel subsystems. No change in functionality is intended.
There's also other smaller changes and cleanups.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'locking-core-2020-06-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
"The biggest change to core locking facilities in this cycle is the
introduction of local_lock_t - this primitive comes from the -rt
project and identifies CPU-local locking dependencies normally handled
opaquely beind preempt_disable() or local_irq_save/disable() critical
sections.
The generated code on mainline kernels doesn't change as a result, but
still there are benefits: improved debugging and better documentation
of data structure accesses.
The new local_lock_t primitives are introduced and then utilized in a
couple of kernel subsystems. No change in functionality is intended.
There's also other smaller changes and cleanups"
* tag 'locking-core-2020-06-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
zram: Use local lock to protect per-CPU data
zram: Allocate struct zcomp_strm as per-CPU memory
connector/cn_proc: Protect send_msg() with a local lock
squashfs: Make use of local lock in multi_cpu decompressor
mm/swap: Use local_lock for protection
radix-tree: Use local_lock for protection
locking: Introduce local_lock()
locking/lockdep: Replace zero-length array with flexible-array
locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed()
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200507185804.GA15036@embeddedor
These functions are called {early,late} in nmi_{enter,exit} and should
not be traced or probed. They are also puny, so 'inline' them.
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Link: https://lkml.kernel.org/r/20200505134101.048523500@linutronix.de
Force inlining and prevent instrumentation of all sorts by marking the
functions which are invoked from low level entry code with 'noinstr'.
Split the irqflags tracking into two parts. One which does the heavy
lifting while RCU is watching and the final one which can be invoked after
RCU is turned off.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Link: https://lkml.kernel.org/r/20200505134100.484532537@linutronix.de
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Merge tag 'v5.7-rc1' into locking/kcsan, to resolve conflicts and refresh
Resolve these conflicts:
arch/x86/Kconfig
arch/x86/kernel/Makefile
Do a minor "evil merge" to move the KCSAN entry up a bit by a few lines
in the Kconfig to reduce the probability of future conflicts.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The 'invalid wait context' splat doesn't print all the information
required to reconstruct / validate the error, specifically the
irq-context state is missing.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The following commit:
7f26482a87 ("locking/percpu-rwsem: Remove the embedded rwsem")
introduced task_struct memory leaks due to messing up the task_struct
refcount.
At the beginning of percpu_rwsem_wake_function(), it calls get_task_struct(),
but if the trylock failed, it will remain in the waitqueue. However, it
will run percpu_rwsem_wake_function() again with get_task_struct() to
increase the refcount but then only call put_task_struct() once the trylock
succeeded.
Fix it by adjusting percpu_rwsem_wake_function() a bit to guard against
when percpu_rwsem_wait() observing !private, terminating the wait and
doing a quick exit() while percpu_rwsem_wake_function() then doing
wake_up_process(p) as a use-after-free.
Fixes: 7f26482a87 ("locking/percpu-rwsem: Remove the embedded rwsem")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200330213002.2374-1-cai@lca.pw
- Convert the 32bit syscalls to be pt_regs based which removes the
requirement to push all 6 potential arguments onto the stack and
consolidates the interface with the 64bit variant
- The first small portion of the exception and syscall related entry
code consolidation which aims to address the recently discovered
issues vs. RCU, int3, NMI and some other exceptions which can
interrupt any context. The bulk of the changes is still work in
progress and aimed for 5.8.
- A few lockdep namespace cleanups which have been applied into this
branch to keep the prerequisites for the ongoing work confined.
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Merge tag 'x86-entry-2020-03-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 entry code updates from Thomas Gleixner:
- Convert the 32bit syscalls to be pt_regs based which removes the
requirement to push all 6 potential arguments onto the stack and
consolidates the interface with the 64bit variant
- The first small portion of the exception and syscall related entry
code consolidation which aims to address the recently discovered
issues vs. RCU, int3, NMI and some other exceptions which can
interrupt any context. The bulk of the changes is still work in
progress and aimed for 5.8.
- A few lockdep namespace cleanups which have been applied into this
branch to keep the prerequisites for the ongoing work confined.
* tag 'x86-entry-2020-03-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (35 commits)
x86/entry: Fix build error x86 with !CONFIG_POSIX_TIMERS
lockdep: Rename trace_{hard,soft}{irq_context,irqs_enabled}()
lockdep: Rename trace_softirqs_{on,off}()
lockdep: Rename trace_hardirq_{enter,exit}()
x86/entry: Rename ___preempt_schedule
x86: Remove unneeded includes
x86/entry: Drop asmlinkage from syscalls
x86/entry/32: Enable pt_regs based syscalls
x86/entry/32: Use IA32-specific wrappers for syscalls taking 64-bit arguments
x86/entry/32: Rename 32-bit specific syscalls
x86/entry/32: Clean up syscall_32.tbl
x86/entry: Remove ABI prefixes from functions in syscall tables
x86/entry/64: Add __SYSCALL_COMMON()
x86/entry: Remove syscall qualifier support
x86/entry/64: Remove ptregs qualifier from syscall table
x86/entry: Move max syscall number calculation to syscallhdr.sh
x86/entry/64: Split X32 syscall table into its own file
x86/entry/64: Move sys_ni_syscall stub to common.c
x86/entry/64: Use syscall wrappers for x32_rt_sigreturn
x86/entry: Refactor SYS_NI macros
...
Pull locking updates from Ingo Molnar:
"The main changes in this cycle were:
- Continued user-access cleanups in the futex code.
- percpu-rwsem rewrite that uses its own waitqueue and atomic_t
instead of an embedded rwsem. This addresses a couple of
weaknesses, but the primary motivation was complications on the -rt
kernel.
- Introduce raw lock nesting detection on lockdep
(CONFIG_PROVE_RAW_LOCK_NESTING=y), document the raw_lock vs. normal
lock differences. This too originates from -rt.
- Reuse lockdep zapped chain_hlocks entries, to conserve RAM
footprint on distro-ish kernels running into the "BUG:
MAX_LOCKDEP_CHAIN_HLOCKS too low!" depletion of the lockdep
chain-entries pool.
- Misc cleanups, smaller fixes and enhancements - see the changelog
for details"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (55 commits)
fs/buffer: Make BH_Uptodate_Lock bit_spin_lock a regular spinlock_t
thermal/x86_pkg_temp: Make pkg_temp_lock a raw_spinlock_t
Documentation/locking/locktypes: Minor copy editor fixes
Documentation/locking/locktypes: Further clarifications and wordsmithing
m68knommu: Remove mm.h include from uaccess_no.h
x86: get rid of user_atomic_cmpxchg_inatomic()
generic arch_futex_atomic_op_inuser() doesn't need access_ok()
x86: don't reload after cmpxchg in unsafe_atomic_op2() loop
x86: convert arch_futex_atomic_op_inuser() to user_access_begin/user_access_end()
objtool: whitelist __sanitizer_cov_trace_switch()
[parisc, s390, sparc64] no need for access_ok() in futex handling
sh: no need of access_ok() in arch_futex_atomic_op_inuser()
futex: arch_futex_atomic_op_inuser() calling conventions change
completion: Use lockdep_assert_RT_in_threaded_ctx() in complete_all()
lockdep: Add posixtimer context tracing bits
lockdep: Annotate irq_work
lockdep: Add hrtimer context tracing bits
lockdep: Introduce wait-type checks
completion: Use simple wait queues
sched/swait: Prepare usage in completions
...
Continue what commit:
d820ac4c2f ("locking: rename trace_softirq_[enter|exit] => lockdep_softirq_[enter|exit]")
started, rename these to avoid confusing them with tracepoints.
git grep -l "trace_\(soft\|hard\)\(irq_context\|irqs_enabled\)" | while read file;
do
sed -ie 's/trace_\(soft\|hard\)\(irq_context\|irqs_enabled\)/lockdep_\1\2/g' $file;
done
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20200320115859.178626842@infradead.org
Continue what commit:
d820ac4c2f ("locking: rename trace_softirq_[enter|exit] => lockdep_softirq_[enter|exit]")
started, rename these to avoid confusing them with tracepoints.
git grep -l "trace_softirqs_\(on\|off\)" | while read file;
do
sed -ie 's/trace_softirqs_\(on\|off\)/lockdep_softirqs_\1/g' $file;
done
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20200320115859.119434738@infradead.org
Set current->irq_config = 1 for hrtimers which are not marked to expire in
hard interrupt context during hrtimer_init(). These timers will expire in
softirq context on PREEMPT_RT.
Setting this allows lockdep to differentiate these timers. If a timer is
marked to expire in hard interrupt context then the timer callback is not
supposed to acquire a regular spinlock instead of a raw_spinlock in the
expiry callback.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200321113242.534508206@linutronix.de
Extend lockdep to validate lock wait-type context.
The current wait-types are:
LD_WAIT_FREE, /* wait free, rcu etc.. */
LD_WAIT_SPIN, /* spin loops, raw_spinlock_t etc.. */
LD_WAIT_CONFIG, /* CONFIG_PREEMPT_LOCK, spinlock_t etc.. */
LD_WAIT_SLEEP, /* sleeping locks, mutex_t etc.. */
Where lockdep validates that the current lock (the one being acquired)
fits in the current wait-context (as generated by the held stack).
This ensures that there is no attempt to acquire mutexes while holding
spinlocks, to acquire spinlocks while holding raw_spinlocks and so on. In
other words, its a more fancy might_sleep().
Obviously RCU made the entire ordeal more complex than a simple single
value test because RCU can be acquired in (pretty much) any context and
while it presents a context to nested locks it is not the same as it
got acquired in.
Therefore its necessary to split the wait_type into two values, one
representing the acquire (outer) and one representing the nested context
(inner). For most 'normal' locks these two are the same.
[ To make static initialization easier we have the rule that:
.outer == INV means .outer == .inner; because INV == 0. ]
It further means that its required to find the minimal .inner of the held
stack to compare against the outer of the new lock; because while 'normal'
RCU presents a CONFIG type to nested locks, if it is taken while already
holding a SPIN type it obviously doesn't relax the rules.
Below is an example output generated by the trivial test code:
raw_spin_lock(&foo);
spin_lock(&bar);
spin_unlock(&bar);
raw_spin_unlock(&foo);
[ BUG: Invalid wait context ]
-----------------------------
swapper/0/1 is trying to lock:
ffffc90000013f20 (&bar){....}-{3:3}, at: kernel_init+0xdb/0x187
other info that might help us debug this:
1 lock held by swapper/0/1:
#0: ffffc90000013ee0 (&foo){+.+.}-{2:2}, at: kernel_init+0xd1/0x187
The way to read it is to look at the new -{n,m} part in the lock
description; -{3:3} for the attempted lock, and try and match that up to
the held locks, which in this case is the one: -{2,2}.
This tells that the acquiring lock requires a more relaxed environment than
presented by the lock stack.
Currently only the normal locks and RCU are converted, the rest of the
lockdep users defaults to .inner = INV which is ignored. More conversions
can be done when desired.
The check for spinlock_t nesting is not enabled by default. It's a separate
config option for now as there are known problems which are currently
addressed. The config option allows to identify these problems and to
verify that the solutions found are indeed solving them.
The config switch will be removed and the checks will permanently enabled
once the vast majority of issues has been addressed.
[ bigeasy: Move LD_WAIT_FREE,… out of CONFIG_LOCKDEP to avoid compile
failure with CONFIG_DEBUG_SPINLOCK + !CONFIG_LOCKDEP]
[ tglx: Add the config option ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200321113242.427089655@linutronix.de
Extend rcuwait_wait_event() with a state variable so that it is not
restricted to UNINTERRUPTIBLE waits.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200321113241.824030968@linutronix.de
We must avoid any recursion into lockdep if KCSAN is enabled on utilities
used by lockdep. One manifestation of this is corruption of lockdep's
IRQ trace state (if TRACE_IRQFLAGS), resulting in spurious warnings
(see below). This commit fixes this by:
1. Using raw_local_irq{save,restore} in kcsan_setup_watchpoint().
2. Disabling lockdep in kcsan_report().
Tested with:
CONFIG_LOCKDEP=y
CONFIG_DEBUG_LOCKDEP=y
CONFIG_TRACE_IRQFLAGS=y
This fix eliminates spurious warnings such as the following one:
WARNING: CPU: 0 PID: 2 at kernel/locking/lockdep.c:4406 check_flags.part.0+0x101/0x220
Modules linked in:
CPU: 0 PID: 2 Comm: kthreadd Not tainted 5.5.0-rc1+ #11
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
RIP: 0010:check_flags.part.0+0x101/0x220
<snip>
Call Trace:
lock_is_held_type+0x69/0x150
freezer_fork+0x20b/0x370
cgroup_post_fork+0x2c9/0x5c0
copy_process+0x2675/0x3b40
_do_fork+0xbe/0xa30
? _raw_spin_unlock_irqrestore+0x40/0x50
? match_held_lock+0x56/0x250
? kthread_park+0xf0/0xf0
kernel_thread+0xa6/0xd0
? kthread_park+0xf0/0xf0
kthreadd+0x321/0x3d0
? kthread_create_on_cpu+0x130/0x130
ret_from_fork+0x3a/0x50
irq event stamp: 64
hardirqs last enabled at (63): [<ffffffff9a7995d0>] _raw_spin_unlock_irqrestore+0x40/0x50
hardirqs last disabled at (64): [<ffffffff992a96d2>] kcsan_setup_watchpoint+0x92/0x460
softirqs last enabled at (32): [<ffffffff990489b8>] fpu__copy+0xe8/0x470
softirqs last disabled at (30): [<ffffffff99048939>] fpu__copy+0x69/0x470
Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Marco Elver <elver@google.com>
Acked-by: Alexander Potapenko <glider@google.com>
Tested-by: Qian Cai <cai@lca.pw>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
nmi_enter() does lockdep_off() and hence lockdep ignores everything.
And NMI context makes it impossible to do full IN-NMI tracking like we
do IN-HARDIRQ, that could result in graph_lock recursion.
However, since look_up_lock_class() is lockless, we can find the class
of a lock that has prior use and detect IN-NMI after USED, just not
USED after IN-NMI.
NOTE: By shifting the lockdep_off() recursion count to bit-16, we can
easily differentiate between actual recursion and off.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Link: https://lkml.kernel.org/r/20200221134215.090538203@infradead.org
There were two patterns for lockdep_recursion:
Pattern-A:
if (current->lockdep_recursion)
return
current->lockdep_recursion = 1;
/* do stuff */
current->lockdep_recursion = 0;
Pattern-B:
current->lockdep_recursion++;
/* do stuff */
current->lockdep_recursion--;
But a third pattern has emerged:
Pattern-C:
current->lockdep_recursion = 1;
/* do stuff */
current->lockdep_recursion = 0;
And while this isn't broken per-se, it is highly dangerous because it
doesn't nest properly.
Get rid of all Pattern-C instances and shore up Pattern-A with a
warning.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200313093325.GW12561@hirez.programming.kicks-ass.net
Qian Cai reported a bug when PROVE_RCU_LIST=y, and read on /proc/lockdep
triggered a warning:
[ ] DEBUG_LOCKS_WARN_ON(current->hardirqs_enabled)
...
[ ] Call Trace:
[ ] lock_is_held_type+0x5d/0x150
[ ] ? rcu_lockdep_current_cpu_online+0x64/0x80
[ ] rcu_read_lock_any_held+0xac/0x100
[ ] ? rcu_read_lock_held+0xc0/0xc0
[ ] ? __slab_free+0x421/0x540
[ ] ? kasan_kmalloc+0x9/0x10
[ ] ? __kmalloc_node+0x1d7/0x320
[ ] ? kvmalloc_node+0x6f/0x80
[ ] __bfs+0x28a/0x3c0
[ ] ? class_equal+0x30/0x30
[ ] lockdep_count_forward_deps+0x11a/0x1a0
The warning got triggered because lockdep_count_forward_deps() call
__bfs() without current->lockdep_recursion being set, as a result
a lockdep internal function (__bfs()) is checked by lockdep, which is
unexpected, and the inconsistency between the irq-off state and the
state traced by lockdep caused the warning.
Apart from this warning, lockdep internal functions like __bfs() should
always be protected by current->lockdep_recursion to avoid potential
deadlocks and data inconsistency, therefore add the
current->lockdep_recursion on-and-off section to protect __bfs() in both
lockdep_count_forward_deps() and lockdep_count_backward_deps()
Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200312151258.128036-1-boqun.feng@gmail.com
If CPU hotplug testing is enabled, a lock might appear to be maximally
unfair just because one of the CPUs was offline almost all the time.
This commit therefore forgives unfairness if CPU hotplug testing was
enabled.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Both lock_torture_writer() and lock_torture_reader() use the "static"
keyword on their DEFINE_TORTURE_RANDOM(rand) declarations, which means
that a single instance of a random-number generator are shared among all
the writers and another is shared among all the readers. Unfortunately,
this random-number generator was not designed for concurrent access.
This commit therefore removes both "static" keywords so that each reader
and each writer gets its own random-number generator.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The __torture_print_stats() function in locktorture.c carefully
initializes local variable "min" to statp[0].n_lock_acquired, but
then compares it to statp[i].n_lock_fail. Given that the .n_lock_fail
field should normally be zero, and given the initialization, it seems
reasonable to display the maximum and minimum number acquisitions
instead of miscomputing the maximum and minimum number of failures.
This commit therefore switches from failures to acquisitions.
And this turns out to be not only a day-zero bug, but entirely my
own fault. I hate it when that happens!
Fixes: 0af3fe1efa ("locktorture: Add a lock-torture kernel module")
Reported-by: Will Deacon <will@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Peter Zijlstra <peterz@infradead.org>
The rt_mutex structure's ->owner field is read locklessly, so this
commit adds the WRITE_ONCE() to an update in order to provide proper
documentation and READ_ONCE()/WRITE_ONCE() pairing.
This data race was reported by KCSAN. Not appropriate for backporting
due to failure being unlikely.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
We are missing this annotation in percpu_down_write(). Correct
this.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lkml.kernel.org/r/20200108013305.7732-1-dave@stgolabs.net
Now that __percpu_up_read() is only ever used from percpu_up_read()
merge them, it's a small function.
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lkml.kernel.org/r/20200131151540.212415454@infradead.org
Remove the now unused RWSEM_OWNER_UNKNOWN hack. This hack breaks
PREEMPT_RT and getting rid of it was the entire motivation for
re-writing the percpu rwsem.
The biggest problem is that it is fundamentally incompatible with any
form of Priority Inheritance, any exclusively held lock must have a
distinct owner.
Requested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200204092228.GP14946@hirez.programming.kicks-ass.net
The filesystem freezer uses percpu-rwsem in a way that is effectively
write_non_owner() and achieves this with a few horrible hacks that
rely on the rwsem (!percpu) implementation.
When PREEMPT_RT replaces the rwsem implementation with a PI aware
variant this comes apart.
Remove the embedded rwsem and implement it using a waitqueue and an
atomic_t.
- make readers_block an atomic, and use it, with the waitqueue
for a blocking test-and-set write-side.
- have the read-side wait for the 'lock' state to clear.
Have the waiters use FIFO queueing and mark them (reader/writer) with
a new WQ_FLAG. Use a custom wake_function to wake either a single
writer or all readers until a writer.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200204092403.GB14879@hirez.programming.kicks-ass.net
In preparation for removing the embedded rwsem and building a custom
lock, extract the read-trylock primitive.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200131151540.098485539@infradead.org
As preparation to rework __percpu_down_read() move the
__this_cpu_inc() into it.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200131151540.041600199@infradead.org
As preparation for replacing the embedded rwsem, give percpu-rwsem its
own lockdep_map.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200131151539.927625541@infradead.org
Once a lock class is zapped, all the lock chains that include the zapped
class are essentially useless. The lock_chain structure itself can be
reused, but not the corresponding chain_hlocks[] entries. Over time,
we will run out of chain_hlocks entries while there are still plenty
of other lockdep array entries available.
To fix this imbalance, we have to make chain_hlocks entries reusable
just like the others. As the freed chain_hlocks entries are in blocks of
various lengths. A simple bitmap like the one used in the other reusable
lockdep arrays isn't applicable. Instead the chain_hlocks entries are
put into bucketed lists (MAX_CHAIN_BUCKETS) of chain blocks. Bucket 0
is the variable size bucket which houses chain blocks of size larger than
MAX_CHAIN_BUCKETS sorted in decreasing size order. Initially, the whole
array is in one chain block (the primordial chain block) in bucket 0.
The minimum size of a chain block is 2 chain_hlocks entries. That will
be the minimum allocation size. In other word, allocation requests
for one chain_hlocks entry will cause 2-entry block to be returned and
hence 1 entry will be wasted.
Allocation requests for the chain_hlocks are fulfilled first by looking
for chain block of matching size. If not found, the first chain block
from bucket[0] (the largest one) is split. That can cause hlock entries
fragmentation and reduce allocation efficiency if a chain block of size >
MAX_CHAIN_BUCKETS is ever zapped and put back to after the primordial
chain block. So the MAX_CHAIN_BUCKETS must be large enough that this
should seldom happen.
By reusing the chain_hlocks entries, we are able to handle workloads
that add and zap a lot of lock classes without the risk of running out
of chain_hlocks entries as long as the total number of outstanding lock
classes at any time remain within a reasonable limit.
Two new tracking counters, nr_free_chain_hlocks & nr_large_chain_blocks,
are added to track the total number of chain_hlocks entries in the
free bucketed lists and the number of large chain blocks in buckets[0]
respectively. The nr_free_chain_hlocks replaces nr_chain_hlocks.
The nr_large_chain_blocks counter enables to see if we should increase
the number of buckets (MAX_CHAIN_BUCKETS) available so as to avoid to
avoid the fragmentation problem in bucket[0].
An internal nfsd test that ran for more than an hour and kept on
loading and unloading kernel modules could cause the following message
to be displayed.
[ 4318.443670] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
The patched kernel was able to complete the test with a lot of free
chain_hlocks entries to spare:
# cat /proc/lockdep_stats
:
dependency chains: 18867 [max: 65536]
dependency chain hlocks: 74926 [max: 327680]
dependency chain hlocks lost: 0
:
zapped classes: 1541
zapped lock chains: 56765
large chain blocks: 1
By changing MAX_CHAIN_BUCKETS to 3 and add a counter for the size of the
largest chain block. The system still worked and We got the following
lockdep_stats data:
dependency chains: 18601 [max: 65536]
dependency chain hlocks used: 73133 [max: 327680]
dependency chain hlocks lost: 0
:
zapped classes: 1541
zapped lock chains: 56702
large chain blocks: 45165
large chain block size: 20165
By running the test again, I was indeed able to cause chain_hlocks
entries to get lost:
dependency chain hlocks used: 74806 [max: 327680]
dependency chain hlocks lost: 575
:
large chain blocks: 48737
large chain block size: 7
Due to the fragmentation, it is possible that the
"MAX_LOCKDEP_CHAIN_HLOCKS too low!" error can happen even if a lot of
of chain_hlocks entries appear to be free.
Fortunately, a MAX_CHAIN_BUCKETS value of 16 should be big enough that
few variable sized chain blocks, other than the initial one, should
ever be present in bucket 0.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200206152408.24165-7-longman@redhat.com
Add a new counter nr_zapped_lock_chains to track the number lock chains
that have been removed.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200206152408.24165-6-longman@redhat.com
If a lock chain contains a class that is zapped, the whole lock chain is
likely to be invalid. If the zapped class is at the end of the chain,
the partial chain without the zapped class should have been stored
already as the current code will store all its predecessor chains. If
the zapped class is somewhere in the middle, there is no guarantee that
the partial chain will actually happen. It may just clutter up the hash
and make searching slower. I would rather prefer storing the chain only
when it actually happens.
So just dump the corresponding chain_hlocks entries for now. A latter
patch will try to reuse the freed chain_hlocks entries.
This patch also changes the type of nr_chain_hlocks to unsigned integer
to be consistent with the other counters.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200206152408.24165-5-longman@redhat.com
The whole point of the lockdep dynamic key patch is to allow unused
locks to be removed from the lockdep data buffers so that existing
buffer space can be reused. However, there is no way to find out how
many unused locks are zapped and so we don't know if the zapping process
is working properly.
Add a new nr_zapped_classes counter to track that and show it in
/proc/lockdep_stats.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200206152408.24165-4-longman@redhat.com
Currently, the irq_context field of a lock chains displayed in
/proc/lockdep_chains is just a number. It is likely that many people
may not know what a non-zero number means. To make the information more
useful, print the actual irq names ("softirq" and "hardirq") instead.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200206152408.24165-3-longman@redhat.com
There are currently three counters to track the IRQ context of a lock
chain - nr_hardirq_chains, nr_softirq_chains and nr_process_chains.
They are incremented when a new lock chain is added, but they are
not decremented when a lock chain is removed. That causes some of the
statistic counts reported by /proc/lockdep_stats to be incorrect.
IRQ
Fix that by decrementing the right counter when a lock chain is removed.
Since inc_chains() no longer accesses hardirq_context and softirq_context
directly, it is moved out from the CONFIG_TRACE_IRQFLAGS conditional
compilation block.
Fixes: a0b0fd53e1 ("locking/lockdep: Free lock classes that are no longer in use")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200206152408.24165-2-longman@redhat.com
Pull locking updates from Ingo Molnar:
"Just a handful of changes in this cycle: an ARM64 performance
optimization, a comment fix and a debug output fix"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
locking/osq: Use optimized spinning loop for arm64
locking/qspinlock: Fix inaccessible URL of MCS lock paper
locking/lockdep: Fix lockdep_stats indentation problem
Arm64 has a more optimized spinning loop (atomic_cond_read_acquire)
using wfe for spinlock that can boost performance of sibling threads
by putting the current cpu to a wait state that is broken only when
the monitored variable changes or an external event happens.
OSQ has a more complicated spinning loop. Besides the lock value, it
also checks for need_resched() and vcpu_is_preempted(). The check for
need_resched() is not a problem as it is only set by the tick interrupt
handler. That will be detected by the spinning cpu right after iret.
The vcpu_is_preempted() check, however, is a problem as changes to the
preempt state of of previous node will not affect the wait state. For
ARM64, vcpu_is_preempted is not currently defined and so is a no-op.
Will has indicated that he is planning to para-virtualize wfe instead
of defining vcpu_is_preempted for PV support. So just add a comment in
arch/arm64/include/asm/spinlock.h to indicate that vcpu_is_preempted()
should not be defined as suggested.
On a 2-socket 56-core 224-thread ARM64 system, a kernel mutex locking
microbenchmark was run for 10s with and without the patch. The
performance numbers before patch were:
Running locktest with mutex [runtime = 10s, load = 1]
Threads = 224, Min/Mean/Max = 316/123,143/2,121,269
Threads = 224, Total Rate = 2,757 kop/s; Percpu Rate = 12 kop/s
After patch, the numbers were:
Running locktest with mutex [runtime = 10s, load = 1]
Threads = 224, Min/Mean/Max = 334/147,836/1,304,787
Threads = 224, Total Rate = 3,311 kop/s; Percpu Rate = 15 kop/s
So there was about 20% performance improvement.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20200113150735.21956-1-longman@redhat.com
It was found that two lines in the output of /proc/lockdep_stats have
indentation problem:
# cat /proc/lockdep_stats
:
in-process chains: 25057
stack-trace entries: 137827 [max: 524288]
number of stack traces: 7973
number of stack hash chains: 6355
combined max dependencies: 1356414598
hardirq-safe locks: 57
hardirq-unsafe locks: 1286
:
All the numbers displayed in /proc/lockdep_stats except the two stack
trace numbers are formatted with a field with of 11. To properly align
all the numbers, a field width of 11 is now added to the two stack
trace numbers.
Fixes: 8c779229d0 ("locking/lockdep: Report more stack trace statistics")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lkml.kernel.org/r/20191211213139.29934-1-longman@redhat.com
The commit 91d2a812df ("locking/rwsem: Make handoff writer
optimistically spin on owner") will allow a recently woken up waiting
writer to spin on the owner. Unfortunately, if the owner happens to be
RWSEM_OWNER_UNKNOWN, the code will incorrectly spin on it leading to a
kernel crash. This is fixed by passing the proper non-spinnable bits
to rwsem_spin_on_owner() so that RWSEM_OWNER_UNKNOWN will be treated
as a non-spinnable target.
Fixes: 91d2a812df ("locking/rwsem: Make handoff writer optimistically spin on owner")
Reported-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20200115154336.8679-1-longman@redhat.com
If the lockdep code is really running out of the stack_trace entries,
it is likely that buffer overrun can happen and the data immediately
after stack_trace[] will be corrupted.
If there is less than LOCK_TRACE_SIZE_IN_LONGS entries left before
the call to save_trace(), the max_entries computation will leave it
with a very large positive number because of its unsigned nature. The
subsequent call to stack_trace_save() will then corrupt the data after
stack_trace[]. Fix that by changing max_entries to a signed integer
and check for negative value before calling stack_trace_save().
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 12593b7467 ("locking/lockdep: Reduce space occupied by stack traces")
Link: https://lkml.kernel.org/r/20191220135128.14876-1-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This ended up causing some noise in places such as rxrpc running in softirq.
The warning is misleading in this case as the mutex trylock and unlock
operations are done within the same context; and therefore we need not
worry about the PI-boosting issues that comes along with no single-owner
lock guarantees.
While we don't want to support this in mutexes, there is no way out of
this yet; so lets get rid of the WARNs for now, as it is only fair to
code that has historically relied on non-preemptible softirq guarantees.
In addition, changing the lock type is also unviable: exclusive rwsems
have the same issue (just not the WARN_ON) and counting semaphores
would introduce a performance hit as mutexes are a lot more optimized.
This reverts:
a0855d24fc22: ("locking/mutex: Complain upon mutex API misuse in IRQ contexts")
Fixes: a0855d24fc22: ("locking/mutex: Complain upon mutex API misuse in IRQ contexts")
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Tested-by: David Howells <dhowells@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-afs@lists.infradead.org
Cc: linux-fsdevel@vger.kernel.org
Cc: will@kernel.org
Link: https://lkml.kernel.org/r/20191210220523.28540-1-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This fixes various data races in spinlock_debug. By testing with KCSAN,
it is observable that the console gets spammed with data races reports,
suggesting these are extremely frequent.
Example data race report:
read to 0xffff8ab24f403c48 of 4 bytes by task 221 on cpu 2:
debug_spin_lock_before kernel/locking/spinlock_debug.c:85 [inline]
do_raw_spin_lock+0x9b/0x210 kernel/locking/spinlock_debug.c:112
__raw_spin_lock include/linux/spinlock_api_smp.h:143 [inline]
_raw_spin_lock+0x39/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
get_partial_node.isra.0.part.0+0x32/0x2f0 mm/slub.c:1873
get_partial_node mm/slub.c:1870 [inline]
<snip>
write to 0xffff8ab24f403c48 of 4 bytes by task 167 on cpu 3:
debug_spin_unlock kernel/locking/spinlock_debug.c:103 [inline]
do_raw_spin_unlock+0xc9/0x1a0 kernel/locking/spinlock_debug.c:138
__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:159 [inline]
_raw_spin_unlock_irqrestore+0x2d/0x50 kernel/locking/spinlock.c:191
spin_unlock_irqrestore include/linux/spinlock.h:393 [inline]
free_debug_processing+0x1b3/0x210 mm/slub.c:1214
__slab_free+0x292/0x400 mm/slub.c:2864
<snip>
As a side-effect, with KCSAN, this eventually locks up the console, most
likely due to deadlock, e.g. .. -> printk lock -> spinlock_debug ->
KCSAN detects data race -> kcsan_print_report() -> printk lock ->
deadlock.
This fix will 1) avoid the data races, and 2) allow using lock debugging
together with KCSAN.
Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Marco Elver <elver@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20191120155715.28089-1-elver@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull locking updates from Ingo Molnar:
"The main changes in this cycle were:
- A comprehensive rewrite of the robust/PI futex code's exit handling
to fix various exit races. (Thomas Gleixner et al)
- Rework the generic REFCOUNT_FULL implementation using
atomic_fetch_* operations so that the performance impact of the
cmpxchg() loops is mitigated for common refcount operations.
With these performance improvements the generic implementation of
refcount_t should be good enough for everybody - and this got
confirmed by performance testing, so remove ARCH_HAS_REFCOUNT and
REFCOUNT_FULL entirely, leaving the generic implementation enabled
unconditionally. (Will Deacon)
- Other misc changes, fixes, cleanups"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (27 commits)
lkdtm: Remove references to CONFIG_REFCOUNT_FULL
locking/refcount: Remove unused 'refcount_error_report()' function
locking/refcount: Consolidate implementations of refcount_t
locking/refcount: Consolidate REFCOUNT_{MAX,SATURATED} definitions
locking/refcount: Move saturation warnings out of line
locking/refcount: Improve performance of generic REFCOUNT_FULL code
locking/refcount: Move the bulk of the REFCOUNT_FULL implementation into the <linux/refcount.h> header
locking/refcount: Remove unused refcount_*_checked() variants
locking/refcount: Ensure integer operands are treated as signed
locking/refcount: Define constants for saturation and max refcount values
futex: Prevent exit livelock
futex: Provide distinct return value when owner is exiting
futex: Add mutex around futex exit
futex: Provide state handling for exec() as well
futex: Sanitize exit state handling
futex: Mark the begin of futex exit explicitly
futex: Set task::futex_state to DEAD right after handling futex exit
futex: Split futex_mm_release() for exit/exec
exit/exec: Seperate mm_release()
futex: Replace PF_EXITPIDONE with a state
...
This changes "to the list" to "from the list" and also deletes the
obsolete comment about the "@nested" argument.
The "nested" argument was removed in this commit, earlier this year:
5facae4f35 ("locking/lockdep: Remove unused @nested argument from lock_release()").
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20191104091252.GA31509@mwanda
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Add warning checks if mutex_trylock() or mutex_unlock() are used in
IRQ contexts, under CONFIG_DEBUG_MUTEXES=y.
While the mutex rules and semantics are explicitly documented, this allows
to expose any abusers and robustifies the whole thing.
While trylock and unlock are non-blocking, calling from IRQ context
is still forbidden (lock must be within the same context as unlock).
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dave@stgolabs.net
Link: https://lkml.kernel.org/r/20191025033634.3330-1-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Including rwlock.h directly will cause kernel builds to fail
if CONFIG_PREEMPT_RT is defined. The correct header file
(rwlock_rt.h OR rwlock.h) will be included by spinlock.h which
is included by locktorture.c anyway.
Remove the include of linux/rwlock.h.
Signed-off-by: Wolfgang M. Reimer <linuxball@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The strncmp() function is error-prone because it is easy to get the
length wrong, especially if the string is subject to change, especially
given the need to account for the terminating nul byte. This commit
therefore substitutes the newly introduced str_has_prefix(), which
does not require a separately specified length.
Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This patch reverts commit 75437bb304 (locking/pvqspinlock: Don't
wait if vCPU is preempted). A large performance regression was caused
by this commit. on over-subscription scenarios.
The test was run on a Xeon Skylake box, 2 sockets, 40 cores, 80 threads,
with three VMs of 80 vCPUs each. The score of ebizzy -M is reduced from
13000-14000 records/s to 1700-1800 records/s:
Host Guest score
vanilla w/o kvm optimizations upstream 1700-1800 records/s
vanilla w/o kvm optimizations revert 13000-14000 records/s
vanilla w/ kvm optimizations upstream 4500-5000 records/s
vanilla w/ kvm optimizations revert 14000-15500 records/s
Exit from aggressive wait-early mechanism can result in premature yield
and extra scheduling latency.
Actually, only 6% of wait_early events are caused by vcpu_is_preempted()
being true. However, when one vCPU voluntarily releases its vCPU, all
the subsequently waiters in the queue will do the same and the cascading
effect leads to bad performance.
kvm optimizations:
[1] commit d73eb57b80 (KVM: Boost vCPUs that are delivering interrupts)
[2] commit 266e85a5ec (KVM: X86: Boost queue head vCPU to mitigate lock waiter preemption)
Tested-by: loobinliu@tencent.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: loobinliu@tencent.com
Cc: stable@vger.kernel.org
Fixes: 75437bb304 (locking/pvqspinlock: Don't wait if vCPU is preempted)
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Pull scheduler updates from Ingo Molnar:
- MAINTAINERS: Add Mark Rutland as perf submaintainer, Juri Lelli and
Vincent Guittot as scheduler submaintainers. Add Dietmar Eggemann,
Steven Rostedt, Ben Segall and Mel Gorman as scheduler reviewers.
As perf and the scheduler is getting bigger and more complex,
document the status quo of current responsibilities and interests,
and spread the review pain^H^H^H^H fun via an increase in the Cc:
linecount generated by scripts/get_maintainer.pl. :-)
- Add another series of patches that brings the -rt (PREEMPT_RT) tree
closer to mainline: split the monolithic CONFIG_PREEMPT dependencies
into a new CONFIG_PREEMPTION category that will allow the eventual
introduction of CONFIG_PREEMPT_RT. Still a few more hundred patches
to go though.
- Extend the CPU cgroup controller with uclamp.min and uclamp.max to
allow the finer shaping of CPU bandwidth usage.
- Micro-optimize energy-aware wake-ups from O(CPUS^2) to O(CPUS).
- Improve the behavior of high CPU count, high thread count
applications running under cpu.cfs_quota_us constraints.
- Improve balancing with SCHED_IDLE (SCHED_BATCH) tasks present.
- Improve CPU isolation housekeeping CPU allocation NUMA locality.
- Fix deadline scheduler bandwidth calculations and logic when cpusets
rebuilds the topology, or when it gets deadline-throttled while it's
being offlined.
- Convert the cpuset_mutex to percpu_rwsem, to allow it to be used from
setscheduler() system calls without creating global serialization.
Add new synchronization between cpuset topology-changing events and
the deadline acceptance tests in setscheduler(), which were broken
before.
- Rework the active_mm state machine to be less confusing and more
optimal.
- Rework (simplify) the pick_next_task() slowpath.
- Improve load-balancing on AMD EPYC systems.
- ... and misc cleanups, smaller fixes and improvements - please see
the Git log for more details.
* 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (53 commits)
sched/psi: Correct overly pessimistic size calculation
sched/fair: Speed-up energy-aware wake-ups
sched/uclamp: Always use 'enum uclamp_id' for clamp_id values
sched/uclamp: Update CPU's refcount on TG's clamp changes
sched/uclamp: Use TG's clamps to restrict TASK's clamps
sched/uclamp: Propagate system defaults to the root group
sched/uclamp: Propagate parent clamps
sched/uclamp: Extend CPU's cgroup controller
sched/topology: Improve load balancing on AMD EPYC systems
arch, ia64: Make NUMA select SMP
sched, perf: MAINTAINERS update, add submaintainers and reviewers
sched/fair: Use rq_lock/unlock in online_fair_sched_group
cpufreq: schedutil: fix equation in comment
sched: Rework pick_next_task() slow-path
sched: Allow put_prev_task() to drop rq->lock
sched/fair: Expose newidle_balance()
sched: Add task_struct pointer to sched_class::set_curr_task
sched: Rework CPU hotplug task selection
sched/{rt,deadline}: Fix set_next_task vs pick_next_task
sched: Fix kerneldoc comment for ia64_set_curr_task
...
Pull locking updates from Ingo Molnar:
- improve rwsem scalability
- add uninitialized rwsem debugging check
- reduce lockdep's stacktrace memory usage and add diagnostics
- misc cleanups, code consolidation and constification
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
mutex: Fix up mutex_waiter usage
locking/mutex: Use mutex flags macro instead of hard code
locking/mutex: Make __mutex_owner static to mutex.c
locking/qspinlock,x86: Clarify virt_spin_lock_key
locking/rwsem: Check for operations on an uninitialized rwsem
locking/rwsem: Make handoff writer optimistically spin on owner
locking/lockdep: Report more stack trace statistics
locking/lockdep: Reduce space occupied by stack traces
stacktrace: Constify 'entries' arguments
locking/lockdep: Make it clear that what lock_class::key points at is not modified
The patch moving bits into mutex.c was a little too much; by also
moving struct mutex_waiter a few less common CONFIGs would no longer
build.
Fixes: 5f35d5a66b ("locking/mutex: Make __mutex_owner static to mutex.c")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
__mutex_owner() should only be used by the mutex api's.
So, to put this restiction let's move the __mutex_owner()
function definition from linux/mutex.h to mutex.c file.
There exist functions that uses __mutex_owner() like
mutex_is_locked() and mutex_trylock_recursive(), So
to keep legacy thing intact move them as well and
export them.
Move mutex_waiter structure also to keep it private to the
file.
Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: mingo@redhat.com
Cc: will@kernel.org
Link: https://lkml.kernel.org/r/1564585504-3543-1-git-send-email-mojha@codeaurora.org
Currently rwsems is the only locking primitive that lacks this
debug feature. Add it under CONFIG_DEBUG_RWSEMS and do the magic
checking in the locking fastpath (trylock) operation such that
we cover all cases. The unlocking part is pretty straightforward.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: mingo@kernel.org
Cc: Davidlohr Bueso <dave@stgolabs.net>
Link: https://lkml.kernel.org/r/20190729044735.9632-1-dave@stgolabs.net
When the handoff bit is set by a writer, no other tasks other than
the setting writer itself is allowed to acquire the lock. If the
to-be-handoff'ed writer goes to sleep, there will be a wakeup latency
period where the lock is free, but no one can acquire it. That is less
than ideal.
To reduce that latency, the handoff writer will now optimistically spin
on the owner if it happens to be a on-cpu writer. It will spin until
it releases the lock and the to-be-handoff'ed writer can then acquire
the lock immediately without any delay. Of course, if the owner is not
a on-cpu writer, the to-be-handoff'ed writer will have to sleep anyway.
The optimistic spinning code is also modified to not stop spinning
when the handoff bit is set. This will prevent an occasional setting of
handoff bit from causing a bunch of optimistic spinners from entering
into the wait queue causing significant reduction in throughput.
On a 1-socket 22-core 44-thread Skylake system, the AIM7 shared_memory
workload was run with 7000 users. The throughput (jobs/min) of the
following kernels were as follows:
1) 5.2-rc6
- 8,092,486
2) 5.2-rc6 + tip's rwsem patches
- 7,567,568
3) 5.2-rc6 + tip's rwsem patches + this patch
- 7,954,545
Using perf-record(1), the %cpu time used by rwsem_down_write_slowpath(),
rwsem_down_write_failed() and their callees for the 3 kernels were 1.70%,
5.46% and 2.08% respectively.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: x86@kernel.org
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lkml.kernel.org/r/20190625143913.24154-1-longman@redhat.com
Security is a wonderful thing, but so is the ability to debug based on
lockdep warnings. This commit therefore makes lockdep lock addresses
visible in the clear.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Returning the pointer that was passed in allows us to write
slightly more idiomatic code. Convert a few users.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190704221323.24290-1-willy@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Report the number of stack traces and the number of stack trace hash
chains. These two numbers are useful because these allow to estimate
the number of stack trace hash collisions.
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20190722182443.216015-5-bvanassche@acm.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Although commit 669de8bda8 ("kernel/workqueue: Use dynamic lockdep keys
for workqueues") unregisters dynamic lockdep keys when a workqueue is
destroyed, a side effect of that commit is that all stack traces
associated with the lockdep key are leaked when a workqueue is destroyed.
Fix this by storing each unique stack trace once. Other changes in this
patch are:
- Use NULL instead of { .nr_entries = 0 } to represent 'no trace'.
- Store a pointer to a stack trace in struct lock_class and struct
lock_list instead of storing 'nr_entries' and 'offset'.
This patch avoids that the following program triggers the "BUG:
MAX_STACK_TRACE_ENTRIES too low!" complaint:
#include <fcntl.h>
#include <unistd.h>
int main()
{
for (;;) {
int fd = open("/dev/infiniband/rdma_cm", O_RDWR);
close(fd);
}
}
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Reported-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Yuyang Du <duyuyang@gmail.com>
Link: https://lkml.kernel.org/r/20190722182443.216015-4-bvanassche@acm.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This patch does not change the behavior of the lockdep code.
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20190722182443.216015-2-bvanassche@acm.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
An uninitialized/ zeroed mutex will go unnoticed because there is no
check for it. There is a magic check in the unlock's slowpath path which
might go unnoticed if the unlock happens in the fastpath.
Add a ->magic check early in the mutex_lock() and mutex_trylock() path.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190703092125.lsdf4gpsh2plhavb@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
As Will Deacon points out, CONFIG_PROVE_LOCKING implies TRACE_IRQFLAGS,
so the conditions I added in the previous patch, and some others in the
same file can be simplified by only checking for the former.
No functional change.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Yuyang Du <duyuyang@gmail.com>
Fixes: 886532aee3 ("locking/lockdep: Move mark_lock() inside CONFIG_TRACE_IRQFLAGS && CONFIG_PROVE_LOCKING")
Link: https://lkml.kernel.org/r/20190628102919.2345242-1-arnd@arndb.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The usage is now hidden in an #ifdef, so we need to move
the variable itself in there as well to avoid this warning:
kernel/locking/lockdep_proc.c:203:21: error: unused variable 'class' [-Werror,-Wunused-variable]
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qian Cai <cai@lca.pw>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yuyang Du <duyuyang@gmail.com>
Cc: frederic@kernel.org
Fixes: 68d41d8c94 ("locking/lockdep: Fix lock used or unused stats error")
Link: https://lkml.kernel.org/r/20190715092809.736834-1-arnd@arndb.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Since we just reviewed read_slowpath for ACQUIRE correctness, add a
few coments to retain our findings.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
While reviewing another read_slowpath patch, both Will and I noticed
another missing ACQUIRE, namely:
X = 0;
CPU0 CPU1
rwsem_down_read()
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
X = 1;
rwsem_up_write();
rwsem_mark_wake()
atomic_long_add(adjustment, &sem->count);
smp_store_release(&waiter->task, NULL);
if (!waiter.task)
break;
...
}
r = X;
Allows 'r == 0'.
Reported-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reported-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
LTP mtest06 has been observed to occasionally hit "still mapped when
deleted" and following BUG_ON on arm64.
The extra mapcount originated from pagefault handler, which handled
pagefault for vma that has already been detached. vma is detached
under mmap_sem write lock by detach_vmas_to_be_unmapped(), which
also invalidates vmacache.
When the pagefault handler (under mmap_sem read lock) calls
find_vma(), vmacache_valid() wrongly reports vmacache as valid.
After rwsem down_read() returns via 'queue empty' path (as of v5.2),
it does so without an ACQUIRE on sem->count:
down_read()
__down_read()
rwsem_down_read_failed()
__rwsem_down_read_failed_common()
raw_spin_lock_irq(&sem->wait_lock);
if (list_empty(&sem->wait_list)) {
if (atomic_long_read(&sem->count) >= 0) {
raw_spin_unlock_irq(&sem->wait_lock);
return sem;
The problem can be reproduced by running LTP mtest06 in a loop and
building the kernel (-j $NCPUS) in parallel. It does reproduces since
v4.20 on arm64 HPE Apollo 70 (224 CPUs, 256GB RAM, 2 nodes). It
triggers reliably in about an hour.
The patched kernel ran fine for 10+ hours.
Signed-off-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dbueso@suse.de
Fixes: 4b486b535c ("locking/rwsem: Exit read lock slowpath if queue empty & no writer")
Link: https://lkml.kernel.org/r/50b8914e20d1d62bb2dee42d342836c2c16ebee7.1563438048.git.jstancek@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
For writer, the owner value is cleared on unlock. For reader, it is
left intact on unlock for providing better debugging aid on crash dump
and the unlock of one reader may not mean the lock is free.
As a result, the owner_on_cpu() shouldn't be used on read-owner
as the task pointer value may not be valid and it might have
been freed. That is the case in rwsem_spin_on_owner(), but not in
rwsem_can_spin_on_owner(). This can lead to use-after-free error from
KASAN. For example,
BUG: KASAN: use-after-free in rwsem_down_write_slowpath
(/home/miguel/kernel/linux/kernel/locking/rwsem.c:669
/home/miguel/kernel/linux/kernel/locking/rwsem.c:1125)
Fix this by checking for RWSEM_READER_OWNED flag before calling
owner_on_cpu().
Reported-by: Luis Henriques <lhenriques@suse.com>
Tested-by: Luis Henriques <lhenriques@suse.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Fixes: 94a9717b3c ("locking/rwsem: Make rwsem->owner an atomic_long_t")
Link: https://lkml.kernel.org/r/81e82d5b-5074-77e8-7204-28479bbe0df0@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Convert the locking documents to ReST and add them to the
kernel development book where it belongs.
Most of the stuff here is just to make Sphinx to properly
parse the text file, as they're already in good shape,
not requiring massive changes in order to be parsed.
The conversion is actually:
- add blank lines and identation in order to identify paragraphs;
- fix tables markups;
- add some lists markups;
- mark literal blocks;
- adjust title markups.
At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Federico Vaga <federico.vaga@vaga.pv.it>
The stats variable nr_unused_locks is incremented every time a new lock
class is register and decremented when the lock is first used in
__lock_acquire(). And after all, it is shown and checked in lockdep_stats.
However, under configurations that either CONFIG_TRACE_IRQFLAGS or
CONFIG_PROVE_LOCKING is not defined:
The commit:
0918065151 ("locking/lockdep: Consolidate lock usage bit initialization")
missed marking the LOCK_USED flag at IRQ usage initialization because
as mark_usage() is not called. And the commit:
886532aee3 ("locking/lockdep: Move mark_lock() inside CONFIG_TRACE_IRQFLAGS && CONFIG_PROVE_LOCKING")
further made mark_lock() not defined such that the LOCK_USED cannot be
marked at all when the lock is first acquired.
As a result, we fix this by not showing and checking the stats under such
configurations for lockdep_stats.
Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: arnd@arndb.de
Cc: frederic@kernel.org
Link: https://lkml.kernel.org/r/20190709101522.9117-1-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull locking updates from Ingo Molnar:
"The main changes in this cycle are:
- rwsem scalability improvements, phase #2, by Waiman Long, which are
rather impressive:
"On a 2-socket 40-core 80-thread Skylake system with 40 reader
and writer locking threads, the min/mean/max locking operations
done in a 5-second testing window before the patchset were:
40 readers, Iterations Min/Mean/Max = 1,807/1,808/1,810
40 writers, Iterations Min/Mean/Max = 1,807/50,344/151,255
After the patchset, they became:
40 readers, Iterations Min/Mean/Max = 30,057/31,359/32,741
40 writers, Iterations Min/Mean/Max = 94,466/95,845/97,098"
There's a lot of changes to the locking implementation that makes
it similar to qrwlock, including owner handoff for more fair
locking.
Another microbenchmark shows how across the spectrum the
improvements are:
"With a locking microbenchmark running on 5.1 based kernel, the
total locking rates (in kops/s) on a 2-socket Skylake system
with equal numbers of readers and writers (mixed) before and
after this patchset were:
# of Threads Before Patch After Patch
------------ ------------ -----------
2 2,618 4,193
4 1,202 3,726
8 802 3,622
16 729 3,359
32 319 2,826
64 102 2,744"
The changes are extensive and the patch-set has been through
several iterations addressing various locking workloads. There
might be more regressions, but unless they are pathological I
believe we want to use this new implementation as the baseline
going forward.
- jump-label optimizations by Daniel Bristot de Oliveira: the primary
motivation was to remove IPI disturbance of isolated RT-workload
CPUs, which resulted in the implementation of batched jump-label
updates. Beyond the improvement of the real-time characteristics
kernel, in one test this patchset improved static key update
overhead from 57 msecs to just 1.4 msecs - which is a nice speedup
as well.
- atomic64_t cross-arch type cleanups by Mark Rutland: over the last
~10 years of atomic64_t existence the various types used by the
APIs only had to be self-consistent within each architecture -
which means they became wildly inconsistent across architectures.
Mark puts and end to this by reworking all the atomic64
implementations to use 's64' as the base type for atomic64_t, and
to ensure that this type is consistently used for parameters and
return values in the API, avoiding further problems in this area.
- A large set of small improvements to lockdep by Yuyang Du: type
cleanups, output cleanups, function return type and othr cleanups
all around the place.
- A set of percpu ops cleanups and fixes by Peter Zijlstra.
- Misc other changes - please see the Git log for more details"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (82 commits)
locking/lockdep: increase size of counters for lockdep statistics
locking/atomics: Use sed(1) instead of non-standard head(1) option
locking/lockdep: Move mark_lock() inside CONFIG_TRACE_IRQFLAGS && CONFIG_PROVE_LOCKING
x86/jump_label: Make tp_vec_nr static
x86/percpu: Optimize raw_cpu_xchg()
x86/percpu, sched/fair: Avoid local_clock()
x86/percpu, x86/irq: Relax {set,get}_irq_regs()
x86/percpu: Relax smp_processor_id()
x86/percpu: Differentiate this_cpu_{}() and __this_cpu_{}()
locking/rwsem: Guard against making count negative
locking/rwsem: Adaptive disabling of reader optimistic spinning
locking/rwsem: Enable time-based spinning on reader-owned rwsem
locking/rwsem: Make rwsem->owner an atomic_long_t
locking/rwsem: Enable readers spinning on writer
locking/rwsem: Clarify usage of owner's nonspinaable bit
locking/rwsem: Wake up almost all readers in wait queue
locking/rwsem: More optimal RT task handling of null owner
locking/rwsem: Always release wait_lock before waking up tasks
locking/rwsem: Implement lock handoff to prevent lock starvation
locking/rwsem: Make rwsem_spin_on_owner() return owner state
...
When system has been running for a long time, signed integer
counters are not enough for some lockdep statistics. Using
unsigned long counters can satisfy the requirement. Besides,
most of lockdep statistics are unsigned. It is better to use
unsigned int instead of int.
Remove unused variables.
- max_recursion_depth
- nr_cyclic_check_recursions
- nr_find_usage_forwards_recursions
- nr_find_usage_backwards_recursions
Signed-off-by: Kobe Wu <kobe-cp.wu@mediatek.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <linux-mediatek@lists.infradead.org>
Cc: <wsd_upstream@mediatek.com>
Cc: Eason Lin <eason-yh.lin@mediatek.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/1561365348-16050-1-git-send-email-kobe-cp.wu@mediatek.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The last cleanup patch triggered another issue, as now another function
should be moved into the same section:
kernel/locking/lockdep.c:3580:12: error: 'mark_lock' defined but not used [-Werror=unused-function]
static int mark_lock(struct task_struct *curr, struct held_lock *this,
Move mark_lock() into the same #ifdef section as its only caller, and
remove the now-unused mark_lock_irq() stub helper.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Yuyang Du <duyuyang@gmail.com>
Fixes: 0d2cc3b345 ("locking/lockdep: Move valid_state() inside CONFIG_TRACE_IRQFLAGS && CONFIG_PROVE_LOCKING")
Link: https://lkml.kernel.org/r/20190617124718.1232976-1-arnd@arndb.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The upper bits of the count field is used as reader count. When
sufficient number of active readers are present, the most significant
bit will be set and the count becomes negative. If the number of active
readers keep on piling up, we may eventually overflow the reader counts.
This is not likely to happen unless the number of bits reserved for
reader count is reduced because those bits are need for other purpose.
To prevent this count overflow from happening, the most significant
bit is now treated as a guard bit (RWSEM_FLAG_READFAIL). Read-lock
attempts will now fail for both the fast and slow paths whenever this
bit is set. So all those extra readers will be put to sleep in the wait
list. Wakeup will not happen until the reader count reaches 0.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-17-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reader optimistic spinning is helpful when the reader critical section
is short and there aren't that many readers around. It makes readers
relatively more preferred than writers. When a writer times out spinning
on a reader-owned lock and set the nospinnable bits, there are two main
reasons for that.
1) The reader critical section is long, perhaps the task sleeps after
acquiring the read lock.
2) There are just too many readers contending the lock causing it to
take a while to service all of them.
In the former case, long reader critical section will impede the progress
of writers which is usually more important for system performance.
In the later case, reader optimistic spinning tends to make the reader
groups that contain readers that acquire the lock together smaller
leading to more of them. That may hurt performance in some cases. In
other words, the setting of nonspinnable bits indicates that reader
optimistic spinning may not be helpful for those workloads that cause it.
Therefore, any writers that have observed the setting of the writer
nonspinnable bit for a given rwsem after they fail to acquire the lock
via optimistic spinning will set the reader nonspinnable bit once they
acquire the write lock. Similarly, readers that observe the setting
of reader nonspinnable bit at slowpath entry will also set the reader
nonspinnable bit when they acquire the read lock via the wakeup path.
Once the reader nonspinnable bit is on, it will only be reset when
a writer is able to acquire the rwsem in the fast path or somehow a
reader or writer in the slowpath doesn't observe the nonspinable bit.
This is to discourage reader optmistic spinning on that particular
rwsem and make writers more preferred. This adaptive disabling of reader
optimistic spinning will alleviate some of the negative side effect of
this feature.
In addition, this patch tries to make readers in the spinning queue
follow the phase-fair principle after quitting optimistic spinning
by checking if another reader has somehow acquired a read lock after
this reader enters the optimistic spinning queue. If so and the rwsem
is still reader-owned, this reader is in the right read-phase and can
attempt to acquire the lock.
On a 2-socket 40-core 80-thread Skylake system, the page_fault1 test of
the will-it-scale benchmark was run with various number of threads. The
number of operations done before reader optimistic spinning patches,
this patch and after this patch were:
Threads Before rspin Before patch After patch %change
------- ------------ ------------ ----------- -------
20 5541068 5345484 5455667 -3.5%/ +2.1%
40 10185150 7292313 9219276 -28.5%/+26.4%
60 8196733 6460517 7181209 -21.2%/+11.2%
80 9508864 6739559 8107025 -29.1%/+20.3%
This patch doesn't recover all the lost performance, but it is more
than half. Given the fact that reader optimistic spinning does benefit
some workloads, this is a good compromise.
Using the rwsem locking microbenchmark with very short critical section,
this patch doesn't have too much impact on locking performance as shown
by the locking rates (kops/s) below with equal numbers of readers and
writers before and after this patch:
# of Threads Pre-patch Post-patch
------------ --------- ----------
2 4,730 4,969
4 4,814 4,786
8 4,866 4,815
16 4,715 4,511
32 3,338 3,500
64 3,212 3,389
80 3,110 3,044
When running the locking microbenchmark with 40 dedicated reader and writer
threads, however, the reader performance is curtailed to favor the writer.
Before patch:
40 readers, Iterations Min/Mean/Max = 204,026/234,309/254,816
40 writers, Iterations Min/Mean/Max = 88,515/95,884/115,644
After patch:
40 readers, Iterations Min/Mean/Max = 33,813/35,260/36,791
40 writers, Iterations Min/Mean/Max = 95,368/96,565/97,798
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-16-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
When the rwsem is owned by reader, writers stop optimistic spinning
simply because there is no easy way to figure out if all the readers
are actively running or not. However, there are scenarios where
the readers are unlikely to sleep and optimistic spinning can help
performance.
This patch provides a simple mechanism for spinning on a reader-owned
rwsem by a writer. It is a time threshold based spinning where the
allowable spinning time can vary from 10us to 25us depending on the
condition of the rwsem.
When the time threshold is exceeded, the nonspinnable bits will be set
in the owner field to indicate that no more optimistic spinning will
be allowed on this rwsem until it becomes writer owned again. Not even
readers is allowed to acquire the reader-locked rwsem by optimistic
spinning for fairness.
We also want a writer to acquire the lock after the readers hold the
lock for a relatively long time. In order to give preference to writers
under such a circumstance, the single RWSEM_NONSPINNABLE bit is now split
into two - one for reader and one for writer. When optimistic spinning
is disabled, both bits will be set. When the reader count drop down
to 0, the writer nonspinnable bit will be cleared to allow writers to
spin on the lock, but not the readers. When a writer acquires the lock,
it will write its own task structure pointer into sem->owner and clear
the reader nonspinnable bit in the process.
The time taken for each iteration of the reader-owned rwsem spinning
loop varies. Below are sample minimum elapsed times for 16 iterations
of the loop.
System Time for 16 Iterations
------ ----------------------
1-socket Skylake ~800ns
4-socket Broadwell ~300ns
2-socket ThunderX2 (arm64) ~250ns
When the lock cacheline is contended, we can see up to almost 10X
increase in elapsed time. So 25us will be at most 500, 1300 and 1600
iterations for each of the above systems.
With a locking microbenchmark running on 5.1 based kernel, the total
locking rates (in kops/s) on a 8-socket IvyBridge-EX system with
equal numbers of readers and writers before and after this patch were
as follows:
# of Threads Pre-patch Post-patch
------------ --------- ----------
2 1,759 6,684
4 1,684 6,738
8 1,074 7,222
16 900 7,163
32 458 7,316
64 208 520
128 168 425
240 143 474
This patch gives a big boost in performance for mixed reader/writer
workloads.
With 32 locking threads, the rwsem lock event data were:
rwsem_opt_fail=79850
rwsem_opt_nospin=5069
rwsem_opt_rlock=597484
rwsem_opt_wlock=957339
rwsem_sleep_reader=57782
rwsem_sleep_writer=55663
With 64 locking threads, the data looked like:
rwsem_opt_fail=346723
rwsem_opt_nospin=6293
rwsem_opt_rlock=1127119
rwsem_opt_wlock=1400628
rwsem_sleep_reader=308201
rwsem_sleep_writer=72281
So a lot more threads acquired the lock in the slowpath and more threads
went to sleep.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-15-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The rwsem->owner contains not just the task structure pointer, it also
holds some flags for storing the current state of the rwsem. Some of
the flags may have to be atomically updated. To reflect the new reality,
the owner is now changed to an atomic_long_t type.
New helper functions are added to properly separate out the task
structure pointer and the embedded flags.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-14-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This patch enables readers to optimistically spin on a
rwsem when it is owned by a writer instead of going to sleep
directly. The rwsem_can_spin_on_owner() function is extracted
out of rwsem_optimistic_spin() and is called directly by
rwsem_down_read_slowpath() and rwsem_down_write_slowpath().
With a locking microbenchmark running on 5.1 based kernel, the total
locking rates (in kops/s) on a 8-socket IvyBrige-EX system with equal
numbers of readers and writers before and after the patch were as
follows:
# of Threads Pre-patch Post-patch
------------ --------- ----------
4 1,674 1,684
8 1,062 1,074
16 924 900
32 300 458
64 195 208
128 164 168
240 149 143
The performance change wasn't significant in this case, but this change
is required by a follow-on patch.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-13-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Bit 1 of sem->owner (RWSEM_ANONYMOUSLY_OWNED) is used to designate an
anonymous owner - readers or an anonymous writer. The setting of this
anonymous bit is used as an indicator that optimistic spinning cannot
be done on this rwsem.
With the upcoming reader optimistic spinning patches, a reader-owned
rwsem can be spinned on for a limit period of time. We still need
this bit to indicate a rwsem is nonspinnable, but not setting this
bit loses its meaning that the owner is known. So rename the bit
to RWSEM_NONSPINNABLE to clarify its meaning.
This patch also fixes a DEBUG_RWSEMS_WARN_ON() bug in __up_write().
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-12-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
When the front of the wait queue is a reader, other readers
immediately following the first reader will also be woken up at the
same time. However, if there is a writer in between. Those readers
behind the writer will not be woken up.
Because of optimistic spinning, the lock acquisition order is not FIFO
anyway. The lock handoff mechanism will ensure that lock starvation
will not happen.
Assuming that the lock hold times of the other readers still in the
queue will be about the same as the readers that are being woken up,
there is really not much additional cost other than the additional
latency due to the wakeup of additional tasks by the waker. Therefore
all the readers up to a maximum of 256 in the queue are woken up when
the first waiter is a reader to improve reader throughput. This is
somewhat similar in concept to a phase-fair R/W lock.
With a locking microbenchmark running on 5.1 based kernel, the total
locking rates (in kops/s) on a 8-socket IvyBridge-EX system with
equal numbers of readers and writers before and after this patch were
as follows:
# of Threads Pre-Patch Post-patch
------------ --------- ----------
4 1,641 1,674
8 731 1,062
16 564 924
32 78 300
64 38 195
240 50 149
There is no performance gain at low contention level. At high contention
level, however, this patch gives a pretty decent performance boost.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-11-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
An RT task can do optimistic spinning only if the lock holder is
actually running. If the state of the lock holder isn't known, there
is a possibility that high priority of the RT task may block forward
progress of the lock holder if it happens to reside on the same CPU.
This will lead to deadlock. So we have to make sure that an RT task
will not spin on a reader-owned rwsem.
When the owner is temporarily set to NULL, there are two cases
where we may want to continue spinning:
1) The lock owner is in the process of releasing the lock, sem->owner
is cleared but the lock has not been released yet.
2) The lock was free and owner cleared, but another task just comes
in and acquire the lock before we try to get it. The new owner may
be a spinnable writer.
So an RT task is now made to retry one more time to see if it can
acquire the lock or continue spinning on the new owning writer.
When testing on a 8-socket IvyBridge-EX system, the one additional retry
seems to improve locking performance of RT write locking threads under
heavy contentions. The table below shows the locking rates (in kops/s)
with various write locking threads before and after the patch.
Locking threads Pre-patch Post-patch
--------------- --------- -----------
4 2,753 2,608
8 2,529 2,520
16 1,727 1,918
32 1,263 1,956
64 889 1,343
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-10-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
With the use of wake_q, we can do task wakeups without holding the
wait_lock. There is one exception in the rwsem code, though. It is
when the writer in the slowpath detects that there are waiters ahead
but the rwsem is not held by a writer. This can lead to a long wait_lock
hold time especially when a large number of readers are to be woken up.
Remediate this situation by releasing the wait_lock before waking
up tasks and re-acquiring it afterward. The rwsem_try_write_lock()
function is also modified to read the rwsem count directly to avoid
stale count value.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-9-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Because of writer lock stealing, it is possible that a constant
stream of incoming writers will cause a waiting writer or reader to
wait indefinitely leading to lock starvation.
This patch implements a lock handoff mechanism to disable lock stealing
and force lock handoff to the first waiter or waiters (for readers)
in the queue after at least a 4ms waiting period unless it is a RT
writer task which doesn't need to wait. The waiting period is used to
avoid discouraging lock stealing too much to affect performance.
The setting and clearing of the handoff bit is serialized by the
wait_lock. So racing is not possible.
A rwsem microbenchmark was run for 5 seconds on a 2-socket 40-core
80-thread Skylake system with a v5.1 based kernel and 240 write_lock
threads with 5us sleep critical section.
Before the patch, the min/mean/max numbers of locking operations for
the locking threads were 1/7,792/173,696. After the patch, the figures
became 5,842/6,542/7,458. It can be seen that the rwsem became much
more fair, though there was a drop of about 16% in the mean locking
operations done which was a tradeoff of having better fairness.
Making the waiter set the handoff bit right after the first wakeup can
impact performance especially with a mixed reader/writer workload. With
the same microbenchmark with short critical section and equal number of
reader and writer threads (40/40), the reader/writer locking operation
counts with the current patch were:
40 readers, Iterations Min/Mean/Max = 1,793/1,794/1,796
40 writers, Iterations Min/Mean/Max = 1,793/34,956/86,081
By making waiter set handoff bit immediately after wakeup:
40 readers, Iterations Min/Mean/Max = 43/44/46
40 writers, Iterations Min/Mean/Max = 43/1,263/3,191
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-8-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This patch modifies rwsem_spin_on_owner() to return four possible
values to better reflect the state of lock holder which enables us to
make a better decision of what to do next.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-7-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
After merging all the relevant rwsem code into one single file, there
are a number of optimizations and cleanups that can be done:
1) Remove all the EXPORT_SYMBOL() calls for functions that are not
accessed elsewhere.
2) Remove all the __visible tags as none of the functions will be
called from assembly code anymore.
3) Make all the internal functions static.
4) Remove some unneeded blank lines.
5) Remove the intermediate rwsem_down_{read|write}_failed*() functions
and rename __rwsem_down_{read|write}_failed_common() to
rwsem_down_{read|write}_slowpath().
6) Remove "__" prefix of __rwsem_mark_wake().
7) Use atomic_long_try_cmpxchg_acquire() as much as possible.
8) Remove the rwsem_rtrylock and rwsem_wtrylock lock events as they
are not that useful.
That enables the compiler to do better optimization and reduce code
size. The text+data size of rwsem.o on an x86-64 machine with gcc8 was
reduced from 10237 bytes to 5030 bytes with this change.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-6-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Now we only have one implementation of rwsem. Even though we still use
xadd to handle reader locking, we use cmpxchg for writer instead. So
the filename rwsem-xadd.c is not strictly correct. Also no one outside
of the rwsem code need to know the internal implementation other than
function prototypes for two internal functions that are called directly
from percpu-rwsem.c.
So the rwsem-xadd.c and rwsem.h files are now merged into rwsem.c in
the following order:
<upper part of rwsem.h>
<rwsem-xadd.c>
<lower part of rwsem.h>
<rwsem.c>
The rwsem.h file now contains only 2 function declarations for
__up_read() and __down_read().
This is a code relocation patch with no code change at all except
making __up_read() and __down_read() non-static functions so they
can be used by percpu-rwsem.c.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-5-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The current way of using various reader, writer and waiting biases
in the rwsem code are confusing and hard to understand. I have to
reread the rwsem count guide in the rwsem-xadd.c file from time to
time to remind myself how this whole thing works. It also makes the
rwsem code harder to be optimized.
To make rwsem more sane, a new locking scheme similar to the one in
qrwlock is now being used. The atomic long count has the following
bit definitions:
Bit 0 - writer locked bit
Bit 1 - waiters present bit
Bits 2-7 - reserved for future extension
Bits 8-X - reader count (24/56 bits)
The cmpxchg instruction is now used to acquire the write lock. The read
lock is still acquired with xadd instruction, so there is no change here.
This scheme will allow up to 16M/64P active readers which should be
more than enough. We can always use some more reserved bits if necessary.
With that change, we can deterministically know if a rwsem has been
write-locked. Looking at the count alone, however, one cannot determine
for certain if a rwsem is owned by readers or not as the readers that
set the reader count bits may be in the process of backing out. So we
still need the reader-owned bit in the owner field to be sure.
With a locking microbenchmark running on 5.1 based kernel, the total
locking rates (in kops/s) of the benchmark on a 8-socket 120-core
IvyBridge-EX system before and after the patch were as follows:
Before Patch After Patch
# of Threads wlock rlock wlock rlock
------------ ----- ----- ----- -----
1 30,659 31,341 31,055 31,283
2 8,909 16,457 9,884 17,659
4 9,028 15,823 8,933 20,233
8 8,410 14,212 7,230 17,140
16 8,217 25,240 7,479 24,607
The locking rates of the benchmark on a Power8 system were as follows:
Before Patch After Patch
# of Threads wlock rlock wlock rlock
------------ ----- ----- ----- -----
1 12,963 13,647 13,275 13,601
2 7,570 11,569 7,902 10,829
4 5,232 5,516 5,466 5,435
8 5,233 3,386 5,467 3,168
The locking rates of the benchmark on a 2-socket ARM64 system were
as follows:
Before Patch After Patch
# of Threads wlock rlock wlock rlock
------------ ----- ----- ----- -----
1 21,495 21,046 21,524 21,074
2 5,293 10,502 5,333 10,504
4 5,325 11,463 5,358 11,631
8 5,391 11,712 5,470 11,680
The performance are roughly the same before and after the patch. There
are run-to-run variations in performance. Runs with higher variances
usually have higher throughput.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-4-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
After the following commit:
59aabfc7e9 ("locking/rwsem: Reduce spinlock contention in wakeup after up_read()/up_write()")
the rwsem_wake() forgoes doing a wakeup if the wait_lock cannot be directly
acquired and an optimistic spinning locker is present. This can help performance
by avoiding spinning on the wait_lock when it is contended.
With the later commit:
133e89ef5e ("locking/rwsem: Enable lockless waiter wakeup(s)")
the performance advantage of the above optimization diminishes as the average
wait_lock hold time become much shorter.
With a later patch that supports rwsem lock handoff, we can no
longer relies on the fact that the presence of an optimistic spinning
locker will ensure that the lock will be acquired by a task soon and
rwsem_wake() will be called later on to wake up waiters. This can lead
to missed wakeup and application hang.
So the original 59aabfc7e9 commit has to be reverted.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-3-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The owner field in the rw_semaphore structure is used primarily for
optimistic spinning. However, identifying the rwsem owner can also be
helpful in debugging as well as tracing locking related issues when
analyzing crash dump. The owner field may also store state information
that can be important to the operation of the rwsem.
So the owner field is now made a permanent member of the rw_semaphore
structure irrespective of CONFIG_RWSEM_SPIN_ON_OWNER.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-2-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Based on 1 normalized pattern(s):
distributed under the terms of the gnu gpl version 2
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-only
has been chosen to replace the boilerplate/reference in 2 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Armijn Hemel <armijn@tjaldur.nl>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190531190115.032570679@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Instead of playing silly games with CONFIG_DEBUG_PREEMPT toggling
between this_cpu_*() and __this_cpu_*() use raw_cpu_*(), which is
exactly what we want here.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190527082326.GP2623@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The sequence
static DEFINE_WW_CLASS(test_ww_class);
struct ww_acquire_ctx ww_ctx;
struct ww_mutex ww_lock_a;
struct ww_mutex ww_lock_b;
struct ww_mutex ww_lock_c;
struct mutex lock_c;
ww_acquire_init(&ww_ctx, &test_ww_class);
ww_mutex_init(&ww_lock_a, &test_ww_class);
ww_mutex_init(&ww_lock_b, &test_ww_class);
ww_mutex_init(&ww_lock_c, &test_ww_class);
mutex_init(&lock_c);
ww_mutex_lock(&ww_lock_a, &ww_ctx);
mutex_lock(&lock_c);
ww_mutex_lock(&ww_lock_b, &ww_ctx);
ww_mutex_lock(&ww_lock_c, &ww_ctx);
mutex_unlock(&lock_c); (*)
ww_mutex_unlock(&ww_lock_c);
ww_mutex_unlock(&ww_lock_b);
ww_mutex_unlock(&ww_lock_a);
ww_acquire_fini(&ww_ctx); (**)
will trigger the following error in __lock_release() when calling
mutex_release() at **:
DEBUG_LOCKS_WARN_ON(depth <= 0)
The problem is that the hlock merging happening at * updates the
references for test_ww_class incorrectly to 3 whereas it should've
updated it to 4 (representing all the instances for ww_ctx and
ww_lock_[abc]).
Fix this by updating the references during merging correctly taking into
account that we can have non-zero references (both for the hlock that we
merge into another hlock or for the hlock we are merging into).
Signed-off-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <ville.syrjala@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20190524201509.9199-2-imre.deak@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The sequence
static DEFINE_WW_CLASS(test_ww_class);
struct ww_acquire_ctx ww_ctx;
struct ww_mutex ww_lock_a;
struct ww_mutex ww_lock_b;
struct mutex lock_c;
struct mutex lock_d;
ww_acquire_init(&ww_ctx, &test_ww_class);
ww_mutex_init(&ww_lock_a, &test_ww_class);
ww_mutex_init(&ww_lock_b, &test_ww_class);
mutex_init(&lock_c);
ww_mutex_lock(&ww_lock_a, &ww_ctx);
mutex_lock(&lock_c);
ww_mutex_lock(&ww_lock_b, &ww_ctx);
mutex_unlock(&lock_c); (*)
ww_mutex_unlock(&ww_lock_b);
ww_mutex_unlock(&ww_lock_a);
ww_acquire_fini(&ww_ctx);
triggers the following WARN in __lock_release() when doing the unlock at *:
DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - 1);
The problem is that the WARN check doesn't take into account the merging
of ww_lock_a and ww_lock_b which results in decreasing curr->lockdep_depth
by 2 not only 1.
Note that the following sequence doesn't trigger the WARN, since there
won't be any hlock merging.
ww_acquire_init(&ww_ctx, &test_ww_class);
ww_mutex_init(&ww_lock_a, &test_ww_class);
ww_mutex_init(&ww_lock_b, &test_ww_class);
mutex_init(&lock_c);
mutex_init(&lock_d);
ww_mutex_lock(&ww_lock_a, &ww_ctx);
mutex_lock(&lock_c);
mutex_lock(&lock_d);
ww_mutex_lock(&ww_lock_b, &ww_ctx);
mutex_unlock(&lock_d);
ww_mutex_unlock(&ww_lock_b);
ww_mutex_unlock(&ww_lock_a);
mutex_unlock(&lock_c);
ww_acquire_fini(&ww_ctx);
In general both of the above two sequences are valid and shouldn't
trigger any lockdep warning.
Fix this by taking the decrement due to the hlock merging into account
during lock release and hlock class re-setting. Merging can't happen
during lock downgrading since there won't be a new possibility to merge
hlocks in that case, so add a WARN if merging still happens then.
Signed-off-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: ville.syrjala@linux.intel.com
Link: https://lkml.kernel.org/r/20190524201509.9199-1-imre.deak@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
In mark_lock_irq(), the following checks are performed:
----------------------------------
| -> | unsafe | read unsafe |
|----------------------------------|
| safe | F B | F* B* |
|----------------------------------|
| read safe | F? B* | - |
----------------------------------
Where:
F: check_usage_forwards
B: check_usage_backwards
*: check enabled by STRICT_READ_CHECKS
?: check enabled by the !dir condition
From checking point of view, the special F? case does not make sense,
whereas it perhaps is made for peroformance concern. As later patch will
address this issue, remove this exception, which makes the checks
consistent later.
With STRICT_READ_CHECKS = 1 which is default, there is no functional
change.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-24-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The new bit can be any possible lock usage except it is garbage, so the
cases in switch can be made simpler. Warn early on if wrong usage bit is
passed without taking locks. No functional change.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-23-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
As Peter has put it all sound and complete for the cause, I simply quote:
"It (check_redundant) was added for cross-release (which has since been
reverted) which would generate a lot of redundant links (IIRC) but
having it makes the reports more convoluted -- basically, if we had an
A-B-C relation, then A-C will not be added to the graph because it is
already covered. This then means any report will include B, even though
a shorter cycle might have been possible."
This would increase the number of direct dependencies. For a simple workload
(make clean; reboot; make vmlinux -j8), the data looks like this:
CONFIG_LOCKDEP_SMALL: direct dependencies: 6926
!CONFIG_LOCKDEP_SMALL: direct dependencies: 9052 (+30.7%)
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-21-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
These two functions now handle different check results themselves. A new
check_path function is added to check whether there is a path in the
dependency graph. No functional change.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-20-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The @nested is not used in __release_lock so remove it despite that it
is not used in lock_release in the first place.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-19-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
In check_deadlock(), the third argument read comes from the second
argument hlock so that it can be removed. No functional change.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-18-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The breadth-first search is implemented as flat-out non-recursive now, but
the comments are still describing it as recursive, update the comments in
that regard.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-16-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
In search of a dependency in the lock graph, there is contant checks for
forward or backward search. Directly reference the field offset of the
struct that differentiates the type of search to avoid those checks.
No functional change.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-15-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
With the change, we can slightly adjust the code to iterate the queue in BFS
search, which simplifies the code. No functional change.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-14-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The element field is an array in struct circular_queue to keep track of locks
in the search. Making it the same type as the locks avoids type cast. Also
fix a typo and elaborate the comment above struct circular_queue.
No functional change.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-13-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The lockdep_map argument in them is not used, remove it.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-11-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
held_lock->class_idx is used to point to the class of the held lock. The
index is shifted by 1 to make index 0 mean no class, which results in class
index shifting back and forth but is not worth doing so.
The reason is: (1) there will be no "no-class" held_lock to begin with, and
(2) index 0 seems to be used for error checking, but if something wrong
indeed happened, the index can't be counted on to distinguish it as that
something won't set the class_idx to 0 on purpose to tell us it is wrong.
Therefore, change the index to start from 0. This saves a lot of
back-and-forth shifts and a class slot back to lock_classes.
Since index 0 is now used for lock class, we change the initial chain key to
-1 to avoid key collision, which is due to the fact that __jhash_mix(0, 0, 0) = 0.
Actually, the initial chain key can be any arbitrary value other than 0.
In addition, a bitmap is maintained to keep track of the used lock classes,
and we check the validity of the held lock against that bitmap.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-10-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Chain keys are computed using Jenkins hash function, which needs an initial
hash to start with. Dedicate a macro to make this clear and configurable. A
later patch changes this initial chain key.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-9-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Despite that there is a lockdep_init_task() which does nothing, lockdep
initiates tasks by assigning lockdep fields and does so inconsistently. Fix
this by using lockdep_init_task().
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-8-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The lock usage bit characters are defined and determined with tricks.
Add some explanation to make it a bit clearer, then adjust the logic to
check the usage, which optimizes the code a bit.
No functional change.
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-4-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Since none of the print_*() function's return value is necessary, change
their return type to void. No functional change.
In cases where an invariable return value is used, this change slightly
improves readability, i.e.:
print_x();
return 0;
is definitely better than:
return print_x(); /* where print_x() always returns 0 */
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-2-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Based on 3 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version this program is distributed in the
hope that it will be useful but without any warranty without even
the implied warranty of merchantability or fitness for a particular
purpose see the gnu general public license for more details
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version [author] [kishon] [vijay] [abraham]
[i] [kishon]@[ti] [com] this program is distributed in the hope that
it will be useful but without any warranty without even the implied
warranty of merchantability or fitness for a particular purpose see
the gnu general public license for more details
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version [author] [graeme] [gregory]
[gg]@[slimlogic] [co] [uk] [author] [kishon] [vijay] [abraham] [i]
[kishon]@[ti] [com] [based] [on] [twl6030]_[usb] [c] [author] [hema]
[hk] [hemahk]@[ti] [com] this program is distributed in the hope
that it will be useful but without any warranty without even the
implied warranty of merchantability or fitness for a particular
purpose see the gnu general public license for more details
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-or-later
has been chosen to replace the boilerplate/reference in 1105 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Richard Fontana <rfontana@redhat.com>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070033.202006027@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Currently, the inter-stutter interval is the same as the stutter duration,
that is, whatever number of jiffies is passed into torture_stutter_init().
This has worked well for quite some time, but the addition of
forward-progress testing to rcutorture can delay processes for several
seconds, which can triple the time that they are stuttered.
This commit therefore adds a second argument to torture_stutter_init()
that specifies the inter-stutter interval. While locktorture preserves
the current behavior, rcutorture uses the RCU CPU stall warning interval
to provide a wider inter-stutter interval.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Now that the RCU flavors have been consolidated, rcu_sync_type makes no
sense because none of internal update functions aside from .held() depend
on gp_type. This commit therefore removes this field and consolidates
the relevant code.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
[ paulmck: Added RCU and RCU-bh checks to rcu_sync_is_idle(). ]
[ paulmck: And applied subsequent feedback from Oleg Nesterov. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
The kernel test robot has reported that the use of __this_cpu_add()
causes bug messages like:
BUG: using __this_cpu_add() in preemptible [00000000] code: ...
Given the imprecise nature of the count and the possibility of resetting
the count and doing the measurement again, this is not really a big
problem to use the unprotected __this_cpu_*() functions.
To make the preemption checking code happy, the this_cpu_*() functions
will be used if CONFIG_DEBUG_PREEMPT is defined.
The imprecise nature of the locking counts are also documented with
the suggestion that we should run the measurement a few times with the
counts reset in between to get a better picture of what is going on
under the hood.
Fixes: a8654596f0 ("locking/rwsem: Enable lock event counting")
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
gcc warns that function print_lock_trace() is unused if
CONFIG_PROVE_LOCKING isn't set:
../kernel/locking/lockdep.c:2820:13: warning: ‘print_lock_trace’ defined but not used [-Wunused-function]
Rework so we remove the function if CONFIG_PROVE_LOCKING isn't set.
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: will.deacon@arm.com
Fixes: c120bce780 ("lockdep: Simplify stack trace handling")
Link: http://lkml.kernel.org/r/20190516191326.27003-1-anders.roxell@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
It is possible to ignore the validation for a certain lock by using:
lockdep_set_novalidate_class()
on it. Each invocation will assign a new name to the class it created
for created __lockdep_no_validate__. That means that once
lockdep_set_novalidate_class() has been used on two locks then
class->name won't match lock->name for the first lock triggering the
warning.
So ignore changed non-matching ->name pointer for the special
__lockdep_no_validate__ class.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190517212234.32611-1-bigeasy@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Based on 1 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version this program is distributed in the
hope that it will be useful but without any warranty without even
the implied warranty of merchantability or fitness for a particular
purpose see the gnu general public license for more details you
should have received a copy of the gnu general public license along
with this program if not you can access it online at http www gnu
org licenses gpl 2 0 html
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-or-later
has been chosen to replace the boilerplate/reference in 1 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Jilayne Lovejoy <opensource@jilayne.com>
Reviewed-by: Steve Winslow <swinslow@gmail.com>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190519154041.430943677@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Add SPDX license identifiers to all files which:
- Have no license information of any form
- Have EXPORT_.*_SYMBOL_GPL inside which was used in the
initial scan/conversion to ignore the file
These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:
GPL-2.0-only
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
During my rwsem testing, it was found that after a down_read(), the
reader count may occasionally become 0 or even negative. Consequently,
a writer may steal the lock at that time and execute with the reader
in parallel thus breaking the mutual exclusion guarantee of the write
lock. In other words, both readers and writer can become rwsem owners
simultaneously.
The current reader wakeup code does it in one pass to clear waiter->task
and put them into wake_q before fully incrementing the reader count.
Once waiter->task is cleared, the corresponding reader may see it,
finish the critical section and do unlock to decrement the count before
the count is incremented. This is not a problem if there is only one
reader to wake up as the count has been pre-incremented by 1. It is
a problem if there are more than one readers to be woken up and writer
can steal the lock.
The wakeup was actually done in 2 passes before the following v4.9 commit:
70800c3c0c ("locking/rwsem: Scan the wait_list for readers only once")
To fix this problem, the wakeup is now done in two passes
again. In the first pass, we collect the readers and count them.
The reader count is then fully incremented. In the second pass, the
waiter->task is then cleared and they are put into wake_q to be woken
up later.
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Fixes: 70800c3c0c ("locking/rwsem: Scan the wait_list for readers only once")
Link: http://lkml.kernel.org/r/20190428212557.13482-2-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Remove mmiowb() from the kernel memory barrier API and instead, for
architectures that need it, hide the barrier inside spin_unlock() when
MMIO has been performed inside the critical section.
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Merge tag 'arm64-mmiowb' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux
Pull mmiowb removal from Will Deacon:
"Remove Mysterious Macro Intended to Obscure Weird Behaviours (mmiowb())
Remove mmiowb() from the kernel memory barrier API and instead, for
architectures that need it, hide the barrier inside spin_unlock() when
MMIO has been performed inside the critical section.
The only relatively recent changes have been addressing review
comments on the documentation, which is in a much better shape thanks
to the efforts of Ben and Ingo.
I was initially planning to split this into two pull requests so that
you could run the coccinelle script yourself, however it's been plain
sailing in linux-next so I've just included the whole lot here to keep
things simple"
* tag 'arm64-mmiowb' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (23 commits)
docs/memory-barriers.txt: Update I/O section to be clearer about CPU vs thread
docs/memory-barriers.txt: Fix style, spacing and grammar in I/O section
arch: Remove dummy mmiowb() definitions from arch code
net/ethernet/silan/sc92031: Remove stale comment about mmiowb()
i40iw: Redefine i40iw_mmiowb() to do nothing
scsi/qla1280: Remove stale comment about mmiowb()
drivers: Remove explicit invocations of mmiowb()
drivers: Remove useless trailing comments from mmiowb() invocations
Documentation: Kill all references to mmiowb()
riscv/mmiowb: Hook up mmwiob() implementation to asm-generic code
powerpc/mmiowb: Hook up mmwiob() implementation to asm-generic code
ia64/mmiowb: Add unconditional mmiowb() to arch_spin_unlock()
mips/mmiowb: Add unconditional mmiowb() to arch_spin_unlock()
sh/mmiowb: Add unconditional mmiowb() to arch_spin_unlock()
m68k/io: Remove useless definition of mmiowb()
nds32/io: Remove useless definition of mmiowb()
x86/io: Remove useless definition of mmiowb()
arm64/io: Remove useless definition of mmiowb()
ARM/io: Remove useless definition of mmiowb()
mmiowb: Hook up mmiowb helpers to spinlocks and generic I/O accessors
...
- Support for kernel address space layout randomization
- Add support for kernel image signature verification
- Convert s390 to the generic get_user_pages_fast code
- Convert s390 to the stack unwind API analog to x86
- Add support for CPU directed interrupts for PCI devices
- Provide support for MIO instructions to the PCI base layer, this
will allow the use of direct PCI mappings in user space code
- Add the basic KVM guest ultravisor interface for protected VMs
- Add AT_HWCAP bits for several new hardware capabilities
- Update the CPU measurement facility counter definitions to SVN 6
- Arnds cleanup patches for his quest to get LLVM compiles working
- A vfio-ccw update with bug fixes and support for halt and clear
- Improvements for the hardware TRNG code
- Another round of cleanup for the QDIO layer
- Numerous cleanups and bug fixes
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Merge tag 's390-5.2-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux
Pull s390 updates from Martin Schwidefsky:
- Support for kernel address space layout randomization
- Add support for kernel image signature verification
- Convert s390 to the generic get_user_pages_fast code
- Convert s390 to the stack unwind API analog to x86
- Add support for CPU directed interrupts for PCI devices
- Provide support for MIO instructions to the PCI base layer, this will
allow the use of direct PCI mappings in user space code
- Add the basic KVM guest ultravisor interface for protected VMs
- Add AT_HWCAP bits for several new hardware capabilities
- Update the CPU measurement facility counter definitions to SVN 6
- Arnds cleanup patches for his quest to get LLVM compiles working
- A vfio-ccw update with bug fixes and support for halt and clear
- Improvements for the hardware TRNG code
- Another round of cleanup for the QDIO layer
- Numerous cleanups and bug fixes
* tag 's390-5.2-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux: (98 commits)
s390/vdso: drop unnecessary cc-ldoption
s390: fix clang -Wpointer-sign warnigns in boot code
s390: drop CONFIG_VIRT_TO_BUS
s390: boot, purgatory: pass $(CLANG_FLAGS) where needed
s390: only build for new CPUs with clang
s390: simplify disabled_wait
s390/ftrace: use HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
s390/unwind: introduce stack unwind API
s390/opcodes: add missing instructions to the disassembler
s390/bug: add entry size to the __bug_table section
s390: use proper expoline sections for .dma code
s390/nospec: rename assembler generated expoline thunks
s390: add missing ENDPROC statements to assembler functions
locking/lockdep: check for freed initmem in static_obj()
s390/kernel: add support for kernel address space layout randomization (KASLR)
s390/kernel: introduce .dma sections
s390/sclp: do not use static sccbs
s390/kprobes: use static buffer for insn_page
s390/kernel: convert SYSCALL and PGM_CHECK handlers to .quad
s390/kernel: build a relocatable kernel
...
Pull locking updates from Ingo Molnar:
"Here are the locking changes in this cycle:
- rwsem unification and simpler micro-optimizations to prepare for
more intrusive (and more lucrative) scalability improvements in
v5.3 (Waiman Long)
- Lockdep irq state tracking flag usage cleanups (Frederic
Weisbecker)
- static key improvements (Jakub Kicinski, Peter Zijlstra)
- misc updates, cleanups and smaller fixes"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (26 commits)
locking/lockdep: Remove unnecessary unlikely()
locking/static_key: Don't take sleeping locks in __static_key_slow_dec_deferred()
locking/static_key: Factor out the fast path of static_key_slow_dec()
locking/static_key: Add support for deferred static branches
locking/lockdep: Test all incompatible scenarios at once in check_irq_usage()
locking/lockdep: Avoid bogus Clang warning
locking/lockdep: Generate LOCKF_ bit composites
locking/lockdep: Use expanded masks on find_usage_*() functions
locking/lockdep: Map remaining magic numbers to lock usage mask names
locking/lockdep: Move valid_state() inside CONFIG_TRACE_IRQFLAGS && CONFIG_PROVE_LOCKING
locking/rwsem: Prevent unneeded warning during locking selftest
locking/rwsem: Optimize rwsem structure for uncontended lock acquisition
locking/rwsem: Enable lock event counting
locking/lock_events: Don't show pvqspinlock events on bare metal
locking/lock_events: Make lock_events available for all archs & other locks
locking/qspinlock_stat: Introduce generic lockevent_*() counting APIs
locking/rwsem: Enhance DEBUG_RWSEMS_WARN_ON() macro
locking/rwsem: Add debug check for __down_read*()
locking/rwsem: Micro-optimize rwsem_try_read_lock_unqueued()
locking/rwsem: Move rwsem internal function declarations to rwsem-xadd.h
...
Pull stack trace updates from Ingo Molnar:
"So Thomas looked at the stacktrace code recently and noticed a few
weirdnesses, and we all know how such stories of crummy kernel code
meeting German engineering perfection end: a 45-patch series to clean
it all up! :-)
Here's the changes in Thomas's words:
'Struct stack_trace is a sinkhole for input and output parameters
which is largely pointless for most usage sites. In fact if embedded
into other data structures it creates indirections and extra storage
overhead for no benefit.
Looking at all usage sites makes it clear that they just require an
interface which is based on a storage array. That array is either on
stack, global or embedded into some other data structure.
Some of the stack depot usage sites are outright wrong, but
fortunately the wrongness just causes more stack being used for
nothing and does not have functional impact.
Another oddity is the inconsistent termination of the stack trace
with ULONG_MAX. It's pointless as the number of entries is what
determines the length of the stored trace. In fact quite some call
sites remove the ULONG_MAX marker afterwards with or without nasty
comments about it. Not all architectures do that and those which do,
do it inconsistenly either conditional on nr_entries == 0 or
unconditionally.
The following series cleans that up by:
1) Removing the ULONG_MAX termination in the architecture code
2) Removing the ULONG_MAX fixups at the call sites
3) Providing plain storage array based interfaces for stacktrace
and stackdepot.
4) Cleaning up the mess at the callsites including some related
cleanups.
5) Removing the struct stack_trace based interfaces
This is not changing the struct stack_trace interfaces at the
architecture level, but it removes the exposure to the generic
code'"
* 'core-stacktrace-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (45 commits)
x86/stacktrace: Use common infrastructure
stacktrace: Provide common infrastructure
lib/stackdepot: Remove obsolete functions
stacktrace: Remove obsolete functions
livepatch: Simplify stack trace retrieval
tracing: Remove the last struct stack_trace usage
tracing: Simplify stack trace retrieval
tracing: Make ftrace_trace_userstack() static and conditional
tracing: Use percpu stack trace buffer more intelligently
tracing: Simplify stacktrace retrieval in histograms
lockdep: Simplify stack trace handling
lockdep: Remove save argument from check_prev_add()
lockdep: Remove unused trace argument from print_circular_bug()
drm: Simplify stacktrace handling
dm persistent data: Simplify stack trace handling
dm bufio: Simplify stack trace retrieval
btrfs: ref-verify: Simplify stack trace retrieval
dma/debug: Simplify stracktrace retrieval
fault-inject: Simplify stacktrace retrieval
mm/page_owner: Simplify stack trace handling
...
DEBUG_LOCKS_WARN_ON() already contains an unlikely(), there is no need
for another one.
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: houtao1@huawei.com
Link: http://lkml.kernel.org/r/1556540791-23110-1-git-send-email-zhengbin13@huawei.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Replace the indirection through struct stack_trace by using the storage
array based interfaces and storing the information is a small lockdep
specific data structure.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: linux-mm@kvack.org
Cc: David Rientjes <rientjes@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: kasan-dev@googlegroups.com
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: iommu@lists.linux-foundation.org
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: David Sterba <dsterba@suse.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: linux-btrfs@vger.kernel.org
Cc: dm-devel@redhat.com
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: intel-gfx@lists.freedesktop.org
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: dri-devel@lists.freedesktop.org
Cc: David Airlie <airlied@linux.ie>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: linux-arch@vger.kernel.org
Link: https://lkml.kernel.org/r/20190425094802.891724020@linutronix.de
The following warning occurred on s390:
WARNING: CPU: 0 PID: 804 at kernel/locking/lockdep.c:1025 lockdep_register_key+0x30/0x150
This is because the check in static_obj() assumes that all memory within
[_stext, _end] belongs to static objects, which at least for s390 isn't
true. The init section is also part of this range, and freeing it allows
the buddy allocator to allocate memory from it. We have virt == phys for
the kernel on s390, so that such allocations would then have addresses
within the range [_stext, _end].
To fix this, introduce arch_is_kernel_initmem_freed(), similar to
arch_is_kernel_text/data(), and add it to the checks in static_obj().
This will always return 0 on architectures that do not define
arch_is_kernel_initmem_freed. On s390, it will return 1 if initmem has
been freed and the address is in the range [__init_begin, __init_end].
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
check_prev_add_irq() tests all incompatible scenarios one after the
other while adding a lock (@next) to a tree dependency (@prev):
LOCK_USED_IN_HARDIRQ vs LOCK_ENABLED_HARDIRQ
LOCK_USED_IN_HARDIRQ_READ vs LOCK_ENABLED_HARDIRQ
LOCK_USED_IN_SOFTIRQ vs LOCK_ENABLED_SOFTIRQ
LOCK_USED_IN_SOFTIRQ_READ vs LOCK_ENABLED_SOFTIRQ
Also for these four scenarios, we must at least iterate the @prev
backward dependency. Then if it matches the relevant LOCK_USED_* bit,
we must also iterate the @next forward dependency.
Therefore in the best case we iterate 4 times, in the worst case 8 times.
A different approach can let us divide the number of branch iterations
by 4:
1) Iterate through @prev backward dependencies and accumulate all the IRQ
uses in a single mask. In the best case where the current lock hasn't
been used in IRQ, we stop here.
2) Iterate through @next forward dependencies and try to find a lock
whose usage is exclusive to the accumulated usages gathered in the
previous step. If we find one (call it @lockA), we have found an
incompatible use, otherwise we stop here. Only bad locking scenario
go further. So a sane verification stop here.
3) Iterate again through @prev backward dependency and find the lock
whose usage matches @lockA in term of incompatibility. Call that
lock @lockB.
4) Report the incompatible usages of @lockA and @lockB
If no incompatible use is found, the verification never goes beyond
step 2 which means at most two iterations.
The following compares the execution measurements of the function
check_prev_add_irq():
Number of calls | Avg (ns) | Stdev (ns) | Total time (ns)
------------------------------------------------------------------------
Mainline 8452 | 2652 | 11962 | 22415143
This patch 8452 | 1518 | 7090 | 12835602
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20190402160244.32434-5-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull RCU and LKMM commits from Paul E. McKenney:
- An LKMM commit adding support for synchronize_srcu_expedited()
- A couple of straggling RCU flavor consolidation updates
- Documentation updates.
- Miscellaneous fixes
- SRCU updates
- RCU CPU stall-warning updates
- Torture-test updates
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Instead of open-coding the bitmasks, generate them using the
lockdep_states.h header.
This prepares for additional states, which would make the manual masks
tedious and error prone.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
In order to optimize check_irq_usage() and factorize all the IRQ usage
validations we'll need to be able to check multiple lock usage bits at
once. Prepare the low level usage mask check functions for that purpose.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20190402160244.32434-4-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Clarify the code with mapping some more constant numbers that haven't
been named after their corresponding LOCK_USAGE_* symbol.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20190402160244.32434-3-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
valid_state() and print_usage_bug*() functions are not used beyond
irq locking correctness checks under CONFIG_TRACE_IRQFLAGS && CONFIG_PROVE_LOCKING.
Sadly the "unused function" warning wouldn't fire because valid_state()
is inline so the unused case has remained unseen until now.
So move them inside the appropriate CONFIG_TRACE_IRQFLAGS && CONFIG_PROVE_LOCKING
section.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20190402160244.32434-2-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
If lockdep_register_key() and lockdep_unregister_key() are called with
debug_locks == false then the following warning is reported:
WARNING: CPU: 2 PID: 15145 at kernel/locking/lockdep.c:4920 lockdep_unregister_key+0x1ad/0x240
That warning is reported because lockdep_unregister_key() ignores the
value of 'debug_locks' and because the behavior of lockdep_register_key()
depends on whether or not 'debug_locks' is set. Fix this inconsistency
by making lockdep_unregister_key() take 'debug_locks' again into
account.
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: shenghui <shhuiw@foxmail.com>
Fixes: 90c1cba2b3 ("locking/lockdep: Zap lock classes even with lock debugging disabled")
Link: http://lkml.kernel.org/r/20190415170538.23491-1-bvanassche@acm.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
No architecture terminates the stack trace with ULONG_MAX anymore. Remove
the cruft.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20190410103644.485737321@linutronix.de
The following commit:
a0b0fd53e1 ("locking/lockdep: Free lock classes that are no longer in use")
changed the behavior of lockdep_free_key_range() from
unconditionally zapping lock classes into only zapping lock classes if
debug_lock == true. Not zapping lock classes if debug_lock == false leaves
dangling pointers in several lockdep datastructures, e.g. lock_class::name
in the all_lock_classes list.
The shell command "cat /proc/lockdep" causes the kernel to iterate the
all_lock_classes list. Hence the "unable to handle kernel paging request" cash
that Shenghui encountered by running cat /proc/lockdep.
Since the new behavior can cause cat /proc/lockdep to crash, restore the
pre-v5.1 behavior.
This patch avoids that cat /proc/lockdep triggers the following crash
with debug_lock == false:
BUG: unable to handle kernel paging request at fffffbfff40ca448
RIP: 0010:__asan_load1+0x28/0x50
Call Trace:
string+0xac/0x180
vsnprintf+0x23e/0x820
seq_vprintf+0x82/0xc0
seq_printf+0x92/0xb0
print_name+0x34/0xb0
l_show+0x184/0x200
seq_read+0x59e/0x6c0
proc_reg_read+0x11f/0x170
__vfs_read+0x4d/0x90
vfs_read+0xc5/0x1f0
ksys_read+0xab/0x130
__x64_sys_read+0x43/0x50
do_syscall_64+0x71/0x210
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Reported-by: shenghui <shhuiw@foxmail.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Fixes: a0b0fd53e1 ("locking/lockdep: Free lock classes that are no longer in use") # v5.1-rc1.
Link: https://lkml.kernel.org/r/20190403233552.124673-1-bvanassche@acm.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Add lock event counting calls so that we can track the number of lock
events happening in the rwsem code.
With CONFIG_LOCK_EVENT_COUNTS on and booting a 4-socket 112-thread x86-64
system, the rwsem counts after system bootup were as follows:
rwsem_opt_fail=261
rwsem_opt_wlock=50636
rwsem_rlock=445
rwsem_rlock_fail=0
rwsem_rlock_fast=22
rwsem_rtrylock=810144
rwsem_sleep_reader=441
rwsem_sleep_writer=310
rwsem_wake_reader=355
rwsem_wake_writer=2335
rwsem_wlock=261
rwsem_wlock_fail=0
rwsem_wtrylock=20583
It can be seen that most of the lock acquisitions in the slowpath were
write-locks in the optimistic spinning code path with no sleeping at
all. For this system, over 97% of the locks are acquired via optimistic
spinning. It illustrates the importance of optimistic spinning in
improving the performance of rwsem.
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-11-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
On bare metal, the pvqspinlock event counts will always be 0. So there
is no point in showing their corresponding debugfs files. So they are
skipped in this case.
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-10-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The QUEUED_LOCK_STAT option to report queued spinlocks event counts
was previously allowed only on x86 architecture. To make the locking
event counting code more useful, it is now renamed to a more generic
LOCK_EVENT_COUNTS config option. This new option will be available to
all the architectures that use qspinlock at the moment.
Other locking code can now start to use the generic locking event
counting code by including lock_events.h and put the new locking event
names into the lock_events_list.h header file.
My experience with lock event counting is that it gives valuable insight
on how the locking code works and what can be done to make it better. I
would like to extend this benefit to other locking code like mutex and
rwsem in the near future.
The PV qspinlock specific code will stay in qspinlock_stat.h. The
locking event counters will now reside in the <debugfs>/lock_event_counts
directory.
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-9-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The percpu event counts used by qspinlock code can be useful for
other locking code as well. So a new set of lockevent_* counting APIs
is introduced with the lock event names extracted out into the new
lock_events_list.h header file for easier addition in the future.
The existing qstat_inc() calls are replaced by either lockevent_inc() or
lockevent_cond_inc() calls.
The qstat_hop() call is renamed to lockevent_pv_hop(). The "reset_counters"
debugfs file is also renamed to ".reset_counts".
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-8-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Currently, the DEBUG_RWSEMS_WARN_ON() macro just dumps a stack trace
when the rwsem isn't in the right state. It does not show the actual
states of the rwsem. This may not be that helpful in the debugging
process.
Enhance the DEBUG_RWSEMS_WARN_ON() macro to also show the current
content of the rwsem count and owner fields to give more information
about what is wrong with the rwsem. The debug_locks_off() function is
called as is done inside DEBUG_LOCKS_WARN_ON().
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-7-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
When rwsem_down_read_failed*() return, the read lock is acquired
indirectly by others. So debug checks are added in __down_read() and
__down_read_killable() to make sure the rwsem is really reader-owned.
The other debug check calls in kernel/locking/rwsem.c except the
one in up_read_non_owner() are also moved over to rwsem-xadd.h.
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-6-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The atomic_long_cmpxchg_acquire() in rwsem_try_read_lock_unqueued() is
replaced by atomic_long_try_cmpxchg_acquire() to simpify the code and
generate slightly better assembly code.
There is no functional change.
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-5-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
We don't need to expose rwsem internal functions which are not supposed
to be called directly from other kernel code.
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-4-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Move all the owner setting code closer to the rwsem-xadd fast paths
directly within rwsem.h file as well as in the slowpaths where owner
setting is done after acquring the lock. This will enable us to add
DEBUG_RWSEMS check in a later patch to make sure that read lock is
really acquired when rwsem_down_read_failed() returns, for instance.
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-3-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The rwsem_down_read_failed*() functions were relocated from above the
optimistic spinning section to below that section. This enables the
reader functions to use optimisitic spinning in future patches. There
is no code change.
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-2-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Removing explicit calls to mmiowb() from driver code means that we must
now call into the generic mmiowb_spin_{lock,unlock}() functions from the
core spinlock code. In order to elide barriers following critical
sections without any I/O writes, we also hook into the asm-generic I/O
routines.
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
In preparation for removing all explicit mmiowb() calls from driver
code, implement a tracking system in asm-generic based loosely on the
PowerPC implementation. This allows architectures with a non-empty
mmiowb() definition to have the barrier automatically inserted in
spin_unlock() following a critical section containing an I/O write.
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Currently, we have two different implementation of rwsem:
1) CONFIG_RWSEM_GENERIC_SPINLOCK (rwsem-spinlock.c)
2) CONFIG_RWSEM_XCHGADD_ALGORITHM (rwsem-xadd.c)
As we are going to use a single generic implementation for rwsem-xadd.c
and no architecture-specific code will be needed, there is no point
in keeping two different implementations of rwsem. In most cases, the
performance of rwsem-spinlock.c will be worse. It also doesn't get all
the performance tuning and optimizations that had been implemented in
rwsem-xadd.c over the years.
For simplication, we are going to remove rwsem-spinlock.c and make all
architectures use a single implementation of rwsem - rwsem-xadd.c.
All references to RWSEM_GENERIC_SPINLOCK and RWSEM_XCHGADD_ALGORITHM
in the code are removed.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-c6x-dev@linux-c6x.org
Cc: linux-m68k@lists.linux-m68k.org
Cc: linux-riscv@lists.infradead.org
Cc: linux-um@lists.infradead.org
Cc: linux-xtensa@linux-xtensa.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: nios2-dev@lists.rocketboards.org
Cc: openrisc@lists.librecores.org
Cc: uclinux-h8-devel@lists.sourceforge.jp
Link: https://lkml.kernel.org/r/20190322143008.21313-3-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
As the generic rwsem-xadd code is using the appropriate acquire and
release versions of the atomic operations, the arch specific rwsem.h
files will not be that much faster than the generic code as long as the
atomic functions are properly implemented. So we can remove those arch
specific rwsem.h and stop building asm/rwsem.h to reduce maintenance
effort.
Currently, only x86, alpha and ia64 have implemented architecture
specific fast paths. I don't have access to alpha and ia64 systems for
testing, but they are legacy systems that are not likely to be updated
to the latest kernel anyway.
By using a rwsem microbenchmark, the total locking rates on a 4-socket
56-core 112-thread x86-64 system before and after the patch were as
follows (mixed means equal # of read and write locks):
Before Patch After Patch
# of Threads wlock rlock mixed wlock rlock mixed
------------ ----- ----- ----- ----- ----- -----
1 29,201 30,143 29,458 28,615 30,172 29,201
2 6,807 13,299 1,171 7,725 15,025 1,804
4 6,504 12,755 1,520 7,127 14,286 1,345
8 6,762 13,412 764 6,826 13,652 726
16 6,693 15,408 662 6,599 15,938 626
32 6,145 15,286 496 5,549 15,487 511
64 5,812 15,495 60 5,858 15,572 60
There were some run-to-run variations for the multi-thread tests. For
x86-64, using the generic C code fast path seems to be a little bit
faster than the assembly version with low lock contention. Looking at
the assembly version of the fast paths, there are assembly to/from C
code wrappers that save and restore all the callee-clobbered registers
(7 registers on x86-64). The assembly generated from the generic C
code doesn't need to do that. That may explain the slight performance
gain here.
The generic asm rwsem.h can also be merged into kernel/locking/rwsem.h
with no code change as no other code other than those under
kernel/locking needs to access the internal rwsem macros and functions.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-c6x-dev@linux-c6x.org
Cc: linux-m68k@lists.linux-m68k.org
Cc: linux-riscv@lists.infradead.org
Cc: linux-um@lists.infradead.org
Cc: linux-xtensa@linux-xtensa.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: nios2-dev@lists.rocketboards.org
Cc: openrisc@lists.librecores.org
Cc: uclinux-h8-devel@lists.sourceforge.jp
Link: https://lkml.kernel.org/r/20190322143008.21313-2-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Currently, lock_torture_cleanup() uses the values of cxt.lwsa and cxt.lrsa
to detect bad parameters that prevented locktorture from initializing,
let alone running. In this case, lock_torture_cleanup() does no cleanup
aside from invoking torture_cleanup_begin() and torture_cleanup_end(),
as required to permit future torture tests to run. However, this
heuristic fails if the run with bad parameters was preceded by a previous
run that actually ran: In this case, both cxt.lwsa and cxt.lrsa will
remain non-zero, which means that the current lock_torture_cleanup()
invocation will be unable to detect the fact that it should skip cleanup,
which can result in charming outcomes such as double frees.
This commit therefore NULLs out both cxt.lwsa and cxt.lrsa at the end
of any run that actually ran.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Josh Triplett <josh@joshtriplett.org>
init_data_structures_once() is called for the first time before RCU has
been initialized. Make sure that init_rcu_head() is called before the
RCU head is used and after RCU has been initialized.
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: longman@redhat.com
Link: https://lkml.kernel.org/r/c20aa0f0-42ab-a884-d931-7d4ec2bf0cdc@acm.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Boqun Feng
Peter Zijlstra
Wang Qing
Linus Torvalds
Waiman Long
Eric W. Biederman
Hou Tao
Paul E. McKenney
Ingo Molnar
Wei Yongjun
Marco Elver
Chris Wilson
Kees Cook
Zhenzhong Duan
Qian Cai
Zou Wei
Thomas Gleixner
Dmitry Safonov
Gustavo A. R. Silva
Alex Shi
Sebastian Andrzej Siewior
Davidlohr Bueso
Alexey Dobriyan
Dan Carpenter
Wolfgang M. Reimer
Chuhong Yuan
Wanpeng Li
Mukesh Ojha
Paul E. McKenney
Matthew Wilcox (Oracle)
Bart Van Assche
Arnd Bergmann
Jan Stancek
Mauro Carvalho Chehab
Yuyang Du
Kobe Wu
Imre Deak
Oleg Nesterov
Anders Roxell
zhengbin
Gerald Schaefer
Frederic Weisbecker
Will Deacon