RCU's expedited grace periods can participate in out-of-memory deadlocks
due to all available system_wq kthreads being blocked and there not being
memory available to create more. This commit prevents such deadlocks
by allocating an RCU-specific workqueue_struct at early boot time, and
providing it with a rescuer to ensure forward progress. This uses the
shiny new init_rescuer() function provided by Tejun (but indirectly).
This commit also causes SRCU to use this new RCU-specific
workqueue_struct. Note that SRCU's use of workqueues never blocks them
waiting for readers, so this should be safe from a forward-progress
viewpoint. Note that this moves SRCU from system_power_efficient_wq
to a normal workqueue. In the unlikely event that this results in
measurable degradation, a separate power-efficient workqueue will be
creates for SRCU.
Reported-by: Prateek Sood <prsood@codeaurora.org>
Reported-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Tejun Heo <tj@kernel.org>
The default values for nreader and nwriter are apparently not all that
user-friendly, resulting in people doing scalability tests that ran all
runs at large scale. This commit therefore makes both the nreaders and
nwriters module default to the number of CPUs, and adds a comment to
rcuperf.c stating that the number of CPUs should be specified using the
nr_cpus kernel boot parameter. This commit also eliminates the redundant
rcuperf scripting specification of default values for these parameters.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The rcu_torture_writer() function adapts to requested testing from module
parameters as well as the function pointers in the structure referenced
by cur_ops. However, as long as the module parameters do not conflict
with the function pointers, this adaptation is silent. This silence can
result in confusion as to exactly what was tested, which could in turn
result in untested RCU code making its way into mainline.
This commit therefore makes rcu_torture_writer() announce exactly which
portions of RCU's API it ends up testing.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
During boot, normal grace periods are processed as expedited. When
rcutorture is built into the kernel, it starts during boot and thus
detects that normal grace periods are unconditionally expedited.
Therefore, rcutorture concludes that there is no point in trying
to dynamically enable expediting, do it disables this aspect of testing,
which is a bit of an overreaction to the temporary boot-time expediting.
This commit therefore rechecks forced expediting throughout the test,
enabling dynamic expediting if normal grace periods are processed
normally at any point.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Currently the rcu_torture_fakewriter() function invokes cur_ops->sync()
and cur_ops->exp_sync() without first checking to see if they are in
fact non-NULL. This results in kernel NULL pointer dereferences when
testing RCU implementations that choose not to provide the full set of
primitives. Given that it is perfectly reasonable to have specialized
RCU implementations that provide only a subset of the RCU API, this is
a bug in rcutorture.
This commit therefore makes rcu_torture_fakewriter() check function
pointers before invoking them, thus allowing it to test subsetted
RCU implementations.
Reported-by: Lihao Liang <lianglihao@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit moves to __func__ for function names and for KBUILD_MODNAME
for module names, all in the name of better resilience to change.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit replaces array-allocation calls to kzalloc() with
equivalent calls to kcalloc().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The code in srcu_gp_end() inserts a delay every 0x3ff grace periods in
order to prevent SRCU grace-period work from consuming an entire CPU
when there is a long sequence of expedited SRCU grace-period requests.
However, all of SRCU's grace-period work is carried out in workqueues,
which are in turn within kthreads, which are automatically throttled as
needed by the scheduler. In particular, if there is plenty of idle time,
there is no point in throttling.
This commit therefore removes the expedited SRCU grace-period throttling.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Of course, compilers will optimize out a dead code. Anyway, remove
any dead code for better readibility.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Currently, given a multi-level srcu_node tree, SRCU can scan the full
set of srcu_data structures at each level when cleaning up after a grace
period. This, though harmless otherwise, represents pointless overhead.
This commit therefore eliminates this overhead by scanning the srcu_data
structures only when traversing the leaf srcu_node structures.
Signed-off-by: Ildar Ismagilov <devix84@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
SRCU checks each srcu_data structure's grace-period number for counter
wrap four times per cycle by default. This frequency guarantees that
normal comparisons will detect potential wrap. However, the expedited
grace-period number is not checked. The consquences are not too horrible
(a failure to expedite a grace period when requested), but it would be
good to avoid such things. This commit therefore adds this check to
the expedited grace-period number.
Signed-off-by: Ildar Ismagilov <devix84@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit moves to __func__ for function names in the name of better
resilience to change.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit reworks the first loop in sync_rcu_exp_select_cpus()
to avoid doing unnecssary stores to other CPUs' rcu_data
structures. This speeds up that first loop by roughly a factor of
two on an old x86 system. In the case where the system is mostly
idle, this loop incurs a large fraction of the overhead of the
synchronize_rcu_expedited(). There is less benefit on busy systems
because the overhead of the smp_call_function_single() in the second
loop dominates in that case.
However, it is not unusual to do configuration chances involving
RCU grace periods (both expedited and normal) while the system is
mostly idle, so this optimization is worth doing.
While we are in the area, this commit also adds parentheses to arguments
used by the for_each_leaf_node_possible_cpu() macro.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
If a CPU is transitioning to or from offline state, an expedited
grace period may undergo a timed wait. This timed wait can unduly
delay grace periods, so this commit adds a trace statement to make
it visible.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit adds more tracing of expedited grace periods to enable
improved debugging of slowdowns.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The srcu_funnel_exp_start() function checks to see if the srcu_struct
structure's expedited grace period counter needs updating to reflect a
newly arrived request for an expedited SRCU grace period. Unfortunately,
the check is backwards, so this commit reverses the sense of the test.
Signed-off-by: Ildar Ismagilov <devix84@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Commits c0b334c5bf and ea9b0c8a26 introduced new sparse warnings
by accessing rcu_node->lock directly and ignoring the __private
marker. Introduce a new wrapper and use it. Also fix a similar problem
in srcutree.c introduced by a3883df393.
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
RCU's nxttail has been optimized to be a rcu_segcblist, which is
a multi-tailed linked list with macros defined for the indexes for
each tail. The indexes have been defined in linux/rcu_segcblist.h,
so this commit removes the redundant definitions in kernel/rcu/tree.h.
Signed-off-by: Liu Changcheng <changcheng.liu@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The kernel/rcu/rcu.h file has a pair of consecutive #ifdefs on
CONFIG_TINY_RCU, so this commit consolidates them, thus saving a few
lines of code.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
It is not always obvious that the stack dump from a starved grace-period
kthread isn't instead that of a CPU stalling the current grace period.
This commit therefore adds a pr_err() flagging these dumps.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The debugfs interface displayed statistics on RCU-pending checks but
this interface has since been removed. This commit therefore removes the
no-longer-used rcu_state structure's ->n_force_qs_lh and ->n_force_qs_ngp
fields along with their updates. (Though the ->n_force_qs_ngp field
was actually not used at all, embarrassingly enough.)
If this information proves necessary in the future, the corresponding
event traces will be added.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The debugfs interface displayed statistics on RCU-pending checks
but this interface has since been removed. This commit therefore
removes the no-longer-used rcu_data structure's ->n_rcu_pending,
->n_rp_core_needs_qs, ->n_rp_report_qs, ->n_rp_cb_ready,
->n_rp_cpu_needs_gp, ->n_rp_gp_completed, ->n_rp_gp_started,
->n_rp_nocb_defer_wakeup, and ->n_rp_need_nothing fields along with
their updates.
If this information proves necessary in the future, the corresponding
event traces will be added.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The debugfs interface displayed statistics on RCU callback invocation but
this interface has since been removed. This commit therefore removes the
no-longer-used rcu_data structure's ->n_cbs_invoked and ->n_nocbs_invoked
fields along with their updates.
If this information proves necessary in the future, the corresponding
event traces will be added.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The debugfs interface displayed statistics on RCU priority boosting,
but this interface has since been removed. This commit therefore
removes the no-longer-used rcu_data structure's ->n_tasks_boosted,
->n_exp_boosts, and ->n_exp_boosts and their updates.
If this information proves necessary in the future, the corresponding
event traces will be added.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
In CONFIG_RCU_NOCB_CPU=y kernels, if the boot parameters indicate that
none of the CPUs should in fact be offloaded, the following somewhat
obtuse message appears:
Offload RCU callbacks from CPUs: .
This commit therefore makes the message at least grammatically correct
in this case:
Offload RCU callbacks from CPUs: (none)
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Since rcu_boot_init_percpu_data() is only called at boot time,
there is no data race and spinlock is not needed.
Signed-off-by: Lihao Liang <lianglihao@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This is mostly updates of the usual driver suspects: arcmsr,
scsi_debug, mpt3sas, lpfc, cxlflash, qla2xxx, aacraid, megaraid_sas,
hisi_sas. We also have a rework of the libsas hotplug handling to
make it more robust, a slew of 32 bit time conversions and fixes, and
a host of the usual minor updates and style changes. The biggest
potential for regressions is the libsas hotplug changes, but so far
they seem stable under testing.
Signed-off-by: James E.J. Bottomley <jejb@linux.vnet.ibm.com>
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Merge tag 'scsi-misc' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi
Pull SCSI updates from James Bottomley:
"This is mostly updates of the usual driver suspects: arcmsr,
scsi_debug, mpt3sas, lpfc, cxlflash, qla2xxx, aacraid, megaraid_sas,
hisi_sas.
We also have a rework of the libsas hotplug handling to make it more
robust, a slew of 32 bit time conversions and fixes, and a host of the
usual minor updates and style changes. The biggest potential for
regressions is the libsas hotplug changes, but so far they seem stable
under testing"
* tag 'scsi-misc' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi: (313 commits)
scsi: qla2xxx: Fix logo flag for qlt_free_session_done()
scsi: arcmsr: avoid do_gettimeofday
scsi: core: Add VENDOR_SPECIFIC sense code definitions
scsi: qedi: Drop cqe response during connection recovery
scsi: fas216: fix sense buffer initialization
scsi: ibmvfc: Remove unneeded semicolons
scsi: hisi_sas: fix a bug in hisi_sas_dev_gone()
scsi: hisi_sas: directly attached disk LED feature for v2 hw
scsi: hisi_sas: devicetree: bindings: add LED feature for v2 hw
scsi: megaraid_sas: NVMe passthrough command support
scsi: megaraid: use ktime_get_real for firmware time
scsi: fnic: use 64-bit timestamps
scsi: qedf: Fix error return code in __qedf_probe()
scsi: devinfo: fix format of the device list
scsi: qla2xxx: Update driver version to 10.00.00.05-k
scsi: qla2xxx: Add XCB counters to debugfs
scsi: qla2xxx: Fix queue ID for async abort with Multiqueue
scsi: qla2xxx: Fix warning for code intentation in __qla24xx_handle_gpdb_event()
scsi: qla2xxx: Fix warning during port_name debug print
scsi: qla2xxx: Fix warning in qla2x00_async_iocb_timeout()
...
The purpose of torture_runnable is to allow rcutorture and locktorture
to be started and stopped via sysfs when they are built into the kernel
(as in not compiled as loadable modules). However, the 0444 permissions
for both instances of torture_runnable prevent this use case from ever
being put into practice. Given that there have been no complaints
about this deficiency, it is reasonable to conclude that no one actually
makes use of this sysfs capability. The perf_runnable module parameter
for rcuperf is in the same situation.
This commit therefore removes both torture_runnable instances as well
as perf_runnable.
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit attempts to make a very rare rcutorture failure happen
more often by increasing the fraction of RCU-preempt read-side critical
sections that are preempted.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit adds a torture_preempt_schedule() that is nothingness
in !PREEMPT builds and is preempt_schedule() otherwise. Then
torture_preempt_schedule() is used to eliminate several ugly #ifdefs,
both in rcutorture and in locktorture.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Currently have_rcu_nocb_mask is used to avoid double allocation of
rcu_nocb_mask during boot up. Due to different representation of
cpumask_var_t on different kernel config CPUMASK=y(or n) it was okay.
But now we have a helper cpumask_available(), which can be utilized
to check whether rcu_nocb_mask has been allocated or not without using
a variable.
Removing the variable also reduces vmlinux size.
Unpatched version:
text data bss dec hex filename
13050393 7852470 14543408 35446271 21cddff vmlinux
Patched version:
text data bss dec hex filename
13050390 7852438 14543408 35446236 21cdddc vmlinux
Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The following statement has for some reason proven non-intuitive:
WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0));
This commit therefore adds a comment that states that this warning
usually triggers in response to a double call_rcu(), which is sort
of like a double free. The comment also suggests building with
CONFIG_DEBUG_OBJECTS_RCU_HEAD=y to track down the double call_rcu().
Reported-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Use of init_rcu_head() and destroy_rcu_head() from modules results in
the following build-time error with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y:
ERROR: "init_rcu_head" [drivers/scsi/scsi_mod.ko] undefined!
ERROR: "destroy_rcu_head" [drivers/scsi/scsi_mod.ko] undefined!
This commit therefore adds EXPORT_SYMBOL_GPL() for each to allow them to
be used by GPL-licensed kernel modules.
Reported-by: Bart Van Assche <Bart.VanAssche@wdc.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Invoking queue_delayed_work() while holding a raw spinlock is forbidden
in -rt kernels, which is exactly what __call_srcu() does, indirectly via
srcu_funnel_gp_start(). This commit therefore downgrades Tree SRCU's
locking from raw to non-raw spinlocks, which works because call_srcu()
is not ever called while holding a raw spinlock.
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The code that checks for non-idle non-nohz_idle-usermode tasks invoking
rcu_eqs_enter() and rcu_eqs_exit() prints a considerable quantity of
helpful information. However, these checks fire rarely, so the extra
complexity is no longer worth it. This commit therefore replaces this
debug code with simple WARN_ON_ONCE() statements.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
There is now only one call to rcu_eqs_exit_common() and there is no other
reason to keep it separate. This commit therefore inlines it into its
sole call site, saving a few lines of code in the process.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
There is now only one call to rcu_eqs_enter_common() and there is no other
reason to keep it separate. This commit therefore inlines it into its
sole call site, saving a few lines of code in the process.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Although ->dynticks_nesting is updated only by process level, it is
accessed from hardirq to check for interrupt-from-idle quiescent states.
Store tearing is thus possible, so this commit applies WRITE_ONCE()
to ->dynticks_nesting stores.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The three RCU_LOCKDEP_WARN() calls in rcu_eqs_enter_common() are
redundant with other lockdep checks, so this commit removes them.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Because the ->dynticks_nesting field now only contains the process-based
nesting level instead of a value encoding both the process nesting level
and the irq "nesting" level, we no longer need a long long, even on
32-bit systems. This commit therefore changes both the ->dynticks_nesting
and ->dynticks_nmi_nesting fields to long.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Now that the irq path uses the rcu_nmi_{enter,exit}() algorithm,
rcu_irq_enter() and rcu_irq_exit() may be used from any context. There is
thus no need for rcu_irq_enter_disabled() and for the checks using it.
This commit therefore eliminates rcu_irq_enter_disabled().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Now that ->dynticks_nesting counts only process-level dyntick-idle
entry and exit, there is no need for the elaborate segmented counter
with its guard fields and overflow checking. This commit therefore
makes ->dynticks_nesting be a simple counter.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
RCU currently uses two different mechanisms for tracking irqs and NMIs.
This is unnecessary complexity: Given that NMIs can nest and given that
RCU's tracking handles such nesting, the NMI tracking mechanism can also
be used to track irqs. This commit therefore defines rcu_irq_enter()
in terms of rcu_nmi_enter() and rcu_irq_exit() in terms of rcu_nmi_exit().
Unfortunately, callers must still distinguish between the irq and NMI
functions because additional actions are taken when an irq interrupts
idle or nohz_full usermode execution, and these actions cannot always
be taken from NMI handlers.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
In preparation for merging dyntick-idle irq handling into the NMI
algorithm, clamp ->dynticks_nmi_nesting value to allow for interrupts
that enter but never leave and vice versa.
It is important that the clamping happen outside of the extended quiescent
state. Otherwise, there will be short windows where irqs and NMIs fail
to convince RCU to start watching.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This is a code-motion-only commit that prepares to define rcu_irq_enter()
in terms of rcu_nmi_enter() and rcu_irq_exit() in terms of rcu_irq_exit().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Paul E. McKenney
Byungchul Park
Ildar Ismagilov
Matthew Wilcox
Liu, Changcheng
Tejun Heo
Lihao Liang
Linus Torvalds
Rakib Mullick