Currently d_move(from, to) does the following:
* name/parent of from <- old name/parent of to, from hashed there
* to is unhashed
* name of to is preserved
* if from used to be detached, to gets detached
* if from used to be attached, parent of to <- old parent of from.
That's both user-visibly bogus and complicates reasoning a lot.
Much saner semantics would be
* name/parent of from <- name/parent of to, from hashed there.
* to is unhashed
* name/parent of to is unchanged.
The price, of course, is that old parent of from might lose a reference.
However,
* all potentially cross-directory callers of d_move() have both
parents pinned directly; typically, dentries themselves are grabbed
only after we have grabbed and locked both parents. IOW, the decrement
of old parent's refcount in case of d_move() won't reach zero.
* __d_move() from d_splice_alias() is done to detached alias.
No refcount decrements in that case
* __d_move() from __d_unalias() *can* get the refcount to zero.
So let's grab a reference to alias' old parent before calling __d_unalias()
and dput() it after we'd dropped rename_lock.
That does make d_splice_alias() potentially blocking. However, it has
no callers in non-sleepable contexts (and the case where we'd grown
that dget/dput pair is _very_ rare, so performance is not an issue).
Another thing that needs adjustment is unlocking in the end of __d_move();
folded it in. And cleaned the remnants of bogus ordering from the
"lock them in the beginning" counterpart - it's never been right and
now (well, for 7 years now) we have that thing always serialized on
rename_lock anyway.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
shrink_dentry_list() holds dentry->d_lock and needs to acquire
dentry->d_inode->i_lock. This cannot be done with a spin_lock()
operation because it's the reverse of the regular lock order.
To avoid ABBA deadlocks it is done with a trylock loop.
Trylock loops are problematic in two scenarios:
1) PREEMPT_RT converts spinlocks to 'sleeping' spinlocks, which are
preemptible. As a consequence the i_lock holder can be preempted
by a higher priority task. If that task executes the trylock loop
it will do so forever and live lock.
2) In virtual machines trylock loops are problematic as well. The
VCPU on which the i_lock holder runs can be scheduled out and a
task on a different VCPU can loop for a whole time slice. In the
worst case this can lead to starvation. Commits 47be61845c
("fs/dcache.c: avoid soft-lockup in dput()") and 046b961b45
("shrink_dentry_list(): take parent's d_lock earlier") are
addressing exactly those symptoms.
Avoid the trylock loop by using dentry_kill(). When pruning ancestors,
the same code applies that is used to kill a dentry in dput(). This
also has the benefit that the locking order is now the same. First
the inode is locked, then the parent.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
In case when trylock in there fails, deal with it directly in
dentry_kill(). Note that in cases when we drop and retake
->d_lock, we need to recheck whether to retain the dentry.
Another thing is that dropping/retaking ->d_lock might have
ended up with negative dentry turning into positive; that,
of course, can happen only once...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
In case of trylock failure don't re-add to the list - drop the locks
and carefully get them in the right order. For shrink_dentry_list(),
somebody having grabbed a reference to dentry means that we can
kick it off-list, so if we find dentry being modified under us we
don't need to play silly buggers with retries anyway - off the list
it is.
The locking logics taken out into a helper of its own; lock_parent()
is no longer used for dentries that can be killed under us.
[fix from Eric Biggers folded]
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
A subsequent patch will modify dentry_kill() to call lock_parent().
Move the dentry_kill() implementation "as is" below lock_parent()
first. This will help simplify the review of the subsequent patch
with dentry_kill() changes.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Commit 0d98439ea3 ("vfs: use lockred "dead" flag to mark unrecoverably
dead dentries") removed the `ref' parameter in dentry_kill() but its
documentation remained. Remove it.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
i_dir_seq is subject to concurrent modification by a cmpxchg or
store-release operation, so ensure that the relaxed access in
d_alloc_parallel uses READ_ONCE.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
If d_alloc_parallel runs concurrently with __d_add, it is possible for
d_alloc_parallel to continuously retry whilst i_dir_seq has been
incremented to an odd value by __d_add:
CPU0:
__d_add
n = start_dir_add(dir);
cmpxchg(&dir->i_dir_seq, n, n + 1) == n
CPU1:
d_alloc_parallel
retry:
seq = smp_load_acquire(&parent->d_inode->i_dir_seq) & ~1;
hlist_bl_lock(b);
bit_spin_lock(0, (unsigned long *)b); // Always succeeds
CPU0:
__d_lookup_done(dentry)
hlist_bl_lock
bit_spin_lock(0, (unsigned long *)b); // Never succeeds
CPU1:
if (unlikely(parent->d_inode->i_dir_seq != seq)) {
hlist_bl_unlock(b);
goto retry;
}
Since the simple bit_spin_lock used to implement hlist_bl_lock does not
provide any fairness guarantees, then CPU1 can starve CPU0 of the lock
and prevent it from reaching end_dir_add(dir), therefore CPU1 cannot
exit its retry loop because the sequence number always has the bottom
bit set.
This patch resolves the livelock by not taking hlist_bl_lock in
d_alloc_parallel if the sequence counter is odd, since any subsequent
masked comparison with i_dir_seq will fail anyway.
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Reported-by: Naresh Madhusudana <naresh.madhusudana@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
In case when dentry passed to lock_parent() is protected from freeing only
by the fact that it's on a shrink list and trylock of parent fails, we
could get hit by __dentry_kill() (and subsequent dentry_kill(parent))
between unlocking dentry and locking presumed parent. We need to recheck
that dentry is alive once we lock both it and parent *and* postpone
rcu_read_unlock() until after that point. Otherwise we could return
a pointer to struct dentry that already is rcu-scheduled for freeing, with
->d_lock held on it; caller's subsequent attempt to unlock it can end
up with memory corruption.
Cc: stable@vger.kernel.org # 3.12+, counting backports
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Pull overlayfs updates from Miklos Szeredi:
"This work from Amir adds NFS export capability to overlayfs. NFS
exporting an overlay filesystem is a challange because we want to keep
track of any copy-up of a file or directory between encoding the file
handle and decoding it.
This is achieved by indexing copied up objects by lower layer file
handle. The index is already used for hard links, this patchset
extends the use to NFS file handle decoding"
* 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs: (51 commits)
ovl: check ERR_PTR() return value from ovl_encode_fh()
ovl: fix regression in fsnotify of overlay merge dir
ovl: wire up NFS export operations
ovl: lookup indexed ancestor of lower dir
ovl: lookup connected ancestor of dir in inode cache
ovl: hash non-indexed dir by upper inode for NFS export
ovl: decode pure lower dir file handles
ovl: decode indexed dir file handles
ovl: decode lower file handles of unlinked but open files
ovl: decode indexed non-dir file handles
ovl: decode lower non-dir file handles
ovl: encode lower file handles
ovl: copy up before encoding non-connectable dir file handle
ovl: encode non-indexed upper file handles
ovl: decode connected upper dir file handles
ovl: decode pure upper file handles
ovl: encode pure upper file handles
ovl: document NFS export
vfs: factor out helpers d_instantiate_anon() and d_alloc_anon()
ovl: store 'has_upper' and 'opaque' as bit flags
...
cache objects. This is good, but still leaves a lot of kernel memory
available to be copied to/from userspace in the face of bugs. To further
restrict what memory is available for copying, this creates a way to
whitelist specific areas of a given slab cache object for copying to/from
userspace, allowing much finer granularity of access control. Slab caches
that are never exposed to userspace can declare no whitelist for their
objects, thereby keeping them unavailable to userspace via dynamic copy
operations. (Note, an implicit form of whitelisting is the use of constant
sizes in usercopy operations and get_user()/put_user(); these bypass all
hardened usercopy checks since these sizes cannot change at runtime.)
This new check is WARN-by-default, so any mistakes can be found over the
next several releases without breaking anyone's system.
The series has roughly the following sections:
- remove %p and improve reporting with offset
- prepare infrastructure and whitelist kmalloc
- update VFS subsystem with whitelists
- update SCSI subsystem with whitelists
- update network subsystem with whitelists
- update process memory with whitelists
- update per-architecture thread_struct with whitelists
- update KVM with whitelists and fix ioctl bug
- mark all other allocations as not whitelisted
- update lkdtm for more sensible test overage
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1
Comment: Kees Cook <kees@outflux.net>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=tzmJ
-----END PGP SIGNATURE-----
Merge tag 'usercopy-v4.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux
Pull hardened usercopy whitelisting from Kees Cook:
"Currently, hardened usercopy performs dynamic bounds checking on slab
cache objects. This is good, but still leaves a lot of kernel memory
available to be copied to/from userspace in the face of bugs.
To further restrict what memory is available for copying, this creates
a way to whitelist specific areas of a given slab cache object for
copying to/from userspace, allowing much finer granularity of access
control.
Slab caches that are never exposed to userspace can declare no
whitelist for their objects, thereby keeping them unavailable to
userspace via dynamic copy operations. (Note, an implicit form of
whitelisting is the use of constant sizes in usercopy operations and
get_user()/put_user(); these bypass all hardened usercopy checks since
these sizes cannot change at runtime.)
This new check is WARN-by-default, so any mistakes can be found over
the next several releases without breaking anyone's system.
The series has roughly the following sections:
- remove %p and improve reporting with offset
- prepare infrastructure and whitelist kmalloc
- update VFS subsystem with whitelists
- update SCSI subsystem with whitelists
- update network subsystem with whitelists
- update process memory with whitelists
- update per-architecture thread_struct with whitelists
- update KVM with whitelists and fix ioctl bug
- mark all other allocations as not whitelisted
- update lkdtm for more sensible test overage"
* tag 'usercopy-v4.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux: (38 commits)
lkdtm: Update usercopy tests for whitelisting
usercopy: Restrict non-usercopy caches to size 0
kvm: x86: fix KVM_XEN_HVM_CONFIG ioctl
kvm: whitelist struct kvm_vcpu_arch
arm: Implement thread_struct whitelist for hardened usercopy
arm64: Implement thread_struct whitelist for hardened usercopy
x86: Implement thread_struct whitelist for hardened usercopy
fork: Provide usercopy whitelisting for task_struct
fork: Define usercopy region in thread_stack slab caches
fork: Define usercopy region in mm_struct slab caches
net: Restrict unwhitelisted proto caches to size 0
sctp: Copy struct sctp_sock.autoclose to userspace using put_user()
sctp: Define usercopy region in SCTP proto slab cache
caif: Define usercopy region in caif proto slab cache
ip: Define usercopy region in IP proto slab cache
net: Define usercopy region in struct proto slab cache
scsi: Define usercopy region in scsi_sense_cache slab cache
cifs: Define usercopy region in cifs_request slab cache
vxfs: Define usercopy region in vxfs_inode slab cache
ufs: Define usercopy region in ufs_inode_cache slab cache
...
Merge KASAN word-at-a-time fixups from Andrey Ryabinin.
The word-at-a-time optimizations have caused headaches for KASAN, since
the whole point is that we access byte streams in bigger chunks, and
KASAN can be unhappy about the potential extra access at the end of the
string.
We used to have a horrible hack in dcache, and then people got
complaints from the strscpy() case. This fixes it all up properly, by
adding an explicit helper for the "access byte stream one word at a
time" case.
* emailed patches from Andrey Ryabinin <aryabinin@virtuozzo.com>:
fs: dcache: Revert "manually unpoison dname after allocation to shut up kasan's reports"
fs/dcache: Use read_word_at_a_time() in dentry_string_cmp()
lib/strscpy: Shut up KASAN false-positives in strscpy()
compiler.h: Add read_word_at_a_time() function.
compiler.h, kasan: Avoid duplicating __read_once_size_nocheck()
This reverts commit df4c0e36f1.
It's no longer needed since dentry_string_cmp() now uses
read_word_at_a_time() to avoid kasan's reports.
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
dentry_string_cmp() performs the word-at-a-time reads from 'cs' and may
read slightly more than it was requested in kmallac(). Normally this
would make KASAN to report out-of-bounds access, but this was
workarounded by commit df4c0e36f1 ("fs: dcache: manually unpoison
dname after allocation to shut up kasan's reports").
This workaround is not perfect, since it allows out-of-bounds access to
dentry's name for all the code, not just in dentry_string_cmp().
So it would be better to use read_word_at_a_time() instead and revert
commit df4c0e36f1.
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull dcache updates from Al Viro:
"Neil Brown's d_move()/d_path() race fix"
* 'work.dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
VFS: close race between getcwd() and d_move()
Pull misc vfs updates from Al Viro:
"All kinds of misc stuff, without any unifying topic, from various
people.
Neil's d_anon patch, several bugfixes, introduction of kvmalloc
analogue of kmemdup_user(), extending bitfield.h to deal with
fixed-endians, assorted cleanups all over the place..."
* 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (28 commits)
alpha: osf_sys.c: use timespec64 where appropriate
alpha: osf_sys.c: fix put_tv32 regression
jffs2: Fix use-after-free bug in jffs2_iget()'s error handling path
dcache: delete unused d_hash_mask
dcache: subtract d_hash_shift from 32 in advance
fs/buffer.c: fold init_buffer() into init_page_buffers()
fs: fold __inode_permission() into inode_permission()
fs: add RWF_APPEND
sctp: use vmemdup_user() rather than badly open-coding memdup_user()
snd_ctl_elem_init_enum_names(): switch to vmemdup_user()
replace_user_tlv(): switch to vmemdup_user()
new primitive: vmemdup_user()
memdup_user(): switch to GFP_USER
eventfd: fold eventfd_ctx_get() into eventfd_ctx_fileget()
eventfd: fold eventfd_ctx_read() into eventfd_read()
eventfd: convert to use anon_inode_getfd()
nfs4file: get rid of pointless include of btrfs.h
uvc_v4l2: clean copyin/copyout up
vme_user: don't use __copy_..._user()
usx2y: don't bother with memdup_user() for 16-byte structure
...
Those helpers are going to be used by overlayfs to implement
NFS export decode.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Directory index entries should have 'upper' xattr pointing to the real
upper dir. Verifying that the upper dir file handle is not stale is
expensive, so only verify stale directory index entries on mount if
NFS export feature is enabled.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
VFS pathnames are stored in the names_cache slab cache, either inline
or across an entire allocation entry (when approaching PATH_MAX). These
are copied to/from userspace, so they must be entirely whitelisted.
cache object allocation:
include/linux/fs.h:
#define __getname() kmem_cache_alloc(names_cachep, GFP_KERNEL)
example usage trace:
strncpy_from_user+0x4d/0x170
getname_flags+0x6f/0x1f0
user_path_at_empty+0x23/0x40
do_mount+0x69/0xda0
SyS_mount+0x83/0xd0
fs/namei.c:
getname_flags(...):
...
result = __getname();
...
kname = (char *)result->iname;
result->name = kname;
len = strncpy_from_user(kname, filename, EMBEDDED_NAME_MAX);
...
if (unlikely(len == EMBEDDED_NAME_MAX)) {
const size_t size = offsetof(struct filename, iname[1]);
kname = (char *)result;
result = kzalloc(size, GFP_KERNEL);
...
result->name = kname;
len = strncpy_from_user(kname, filename, PATH_MAX);
In support of usercopy hardening, this patch defines the entire cache
object in the names_cache slab cache as whitelisted, since it may entirely
hold name strings to be copied to/from userspace.
This patch is verbatim from Brad Spengler/PaX Team's PAX_USERCOPY
whitelisting code in the last public patch of grsecurity/PaX based on my
understanding of the code. Changes or omissions from the original code are
mine and don't reflect the original grsecurity/PaX code.
Signed-off-by: David Windsor <dave@nullcore.net>
[kees: adjust commit log, add usage trace]
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
When a dentry name is short enough, it can be stored directly in the
dentry itself (instead in a separate kmalloc allocation). These dentry
short names, stored in struct dentry.d_iname and therefore contained in
the dentry_cache slab cache, need to be coped to userspace.
cache object allocation:
fs/dcache.c:
__d_alloc(...):
...
dentry = kmem_cache_alloc(dentry_cache, ...);
...
dentry->d_name.name = dentry->d_iname;
example usage trace:
filldir+0xb0/0x140
dcache_readdir+0x82/0x170
iterate_dir+0x142/0x1b0
SyS_getdents+0xb5/0x160
fs/readdir.c:
(called via ctx.actor by dir_emit)
filldir(..., const char *name, ...):
...
copy_to_user(..., name, namlen)
fs/libfs.c:
dcache_readdir(...):
...
next = next_positive(dentry, p, 1)
...
dir_emit(..., next->d_name.name, ...)
In support of usercopy hardening, this patch defines a region in the
dentry_cache slab cache in which userspace copy operations are allowed.
This region is known as the slab cache's usercopy region. Slab caches can
now check that each dynamic copy operation involving cache-managed memory
falls entirely within the slab's usercopy region.
This patch is modified from Brad Spengler/PaX Team's PAX_USERCOPY
whitelisting code in the last public patch of grsecurity/PaX based on my
understanding of the code. Changes or omissions from the original code are
mine and don't reflect the original grsecurity/PaX code.
Signed-off-by: David Windsor <dave@nullcore.net>
[kees: adjust hunks for kmalloc-specific things moved later]
[kees: adjust commit log, provide usage trace]
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
d_move() will call __d_drop() and then __d_rehash()
on the dentry being moved. This creates a small window
when the dentry appears to be unhashed. Many tests
of d_unhashed() are made under ->d_lock and so are safe
from racing with this window, but some aren't.
In particular, getcwd() calls d_unlinked() (which calls
d_unhashed()) without d_lock protection, so it can race.
This races has been seen in practice with lustre, which uses d_move() as
part of name lookup. See:
https://jira.hpdd.intel.com/browse/LU-9735
It could race with a regular rename(), and result in ENOENT instead
of either the 'before' or 'after' name.
The race can be demonstrated with a simple program which
has two threads, one renaming a directory back and forth
while another calls getcwd() within that directory: it should never
fail, but does. See:
https://patchwork.kernel.org/patch/9455345/
We could fix this race by taking d_lock and rechecking when
d_unhashed() reports true. Alternately when can remove the window,
which is the approach this patch takes.
___d_drop() is introduce which does *not* clear d_hash.pprev
so the dentry still appears to be hashed. __d_drop() calls
___d_drop(), then clears d_hash.pprev.
__d_move() now uses ___d_drop() and only clears d_hash.pprev
when not rehashing.
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
The original purpose of the per-superblock d_anon list was to
keep disconnected dentries in the cache between consecutive
requests to the NFS server. Dentries can be disconnected if
a client holds a file open and repeatedly performs IO on it,
and if the server drops the dentry, whether due to memory
pressure, server restart, or "echo 3 > /proc/sys/vm/drop_caches".
This purpose was thwarted by commit 75a6f82a0d ("freeing unlinked
file indefinitely delayed") which caused disconnected dentries
to be freed as soon as their refcount reached zero.
This means that, when a dentry being used by nfsd gets disconnected, a
new one needs to be allocated for every request (unless requests
overlap). As the dentry has no name, no parent, and no children,
there is little of value to cache. As small memory allocations are
typically fast (from per-cpu free lists) this likely has little cost.
This means that the original purpose of s_anon is no longer relevant:
there is no longer any need to keep disconnected dentries on a list so
they appear to be hashed.
However, s_anon now has a new use. When you mount an NFS filesystem,
the dentry stored in s_root is just a placebo. The "real" root dentry
is allocated using d_obtain_root() and so it kept on the s_anon list.
I don't know the reason for this, but suspect it related to NFSv4
where a mount of "server:/some/path" require NFS to look up the root
filehandle on the server, then walk down "/some" and "/path" to get
the filehandle to mount.
Whatever the reason, NFS depends on the s_anon list and on
shrink_dcache_for_umount() pruning all dentries on this list. So we
cannot simply remove s_anon.
We could just leave the code unchanged, but apart from that being
potentially confusing, the (unfair) bit-spin-lock which protects
s_anon can become a bottle neck when lots of disconnected dentries are
being created.
So this patch renames s_anon to s_roots, and stops storing
disconnected dentries on the list. Only dentries obtained with
d_obtain_root() are now stored on this list. There are many fewer of
these (only NFS and NILFS2 use the call, and only during filesystem
mount) so contention on the bit-lock will not be a problem.
Possibly an alternate solution should be found for NFS and NILFS2, but
that would require understanding their needs first.
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Preempt counter APIs have been split out, currently, hardirq.h just
includes irq_enter/exit APIs which are not used by vfs at all.
So, remove the unused hardirq.h.
Signed-off-by: Yang Shi <yang.s@alibaba-inc.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
The code in __d_alloc() carefully orders filling in the NUL character
of the name (and the length, hash, and the name itself) with assigning
of the name itself. However, prepend_name() does not order the accesses
to the ->name and ->len fields, other than on TSO systems. This commit
therefore replaces prepend_name()'s READ_ONCE() of ->name with an
smp_load_acquire(), which orders against the subsequent READ_ONCE() of
->len. Because READ_ONCE() now incorporates smp_read_barrier_depends(),
prepend_name()'s smp_read_barrier_depends() is removed. Finally,
to save a line, the smp_wmb()/store pair in __d_alloc() is replaced
by smp_store_release().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: <linux-fsdevel@vger.kernel.org>
Patch series "kmemcheck: kill kmemcheck", v2.
As discussed at LSF/MM, kill kmemcheck.
KASan is a replacement that is able to work without the limitation of
kmemcheck (single CPU, slow). KASan is already upstream.
We are also not aware of any users of kmemcheck (or users who don't
consider KASan as a suitable replacement).
The only objection was that since KASAN wasn't supported by all GCC
versions provided by distros at that time we should hold off for 2
years, and try again.
Now that 2 years have passed, and all distros provide gcc that supports
KASAN, kill kmemcheck again for the very same reasons.
This patch (of 4):
Remove kmemcheck annotations, and calls to kmemcheck from the kernel.
[alexander.levin@verizon.com: correctly remove kmemcheck call from dma_map_sg_attrs]
Link: http://lkml.kernel.org/r/20171012192151.26531-1-alexander.levin@verizon.com
Link: http://lkml.kernel.org/r/20171007030159.22241-2-alexander.levin@verizon.com
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tim Hansen <devtimhansen@gmail.com>
Cc: Vegard Nossum <vegardno@ifi.uio.no>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
preference to ACCESS_ONCE(), and new code is expected to use one of the
former. So far, there's been no reason to change most existing uses of
ACCESS_ONCE(), as these aren't currently harmful.
However, for some features it is necessary to instrument reads and
writes separately, which is not possible with ACCESS_ONCE(). This
distinction is critical to correct operation.
It's possible to transform the bulk of kernel code using the Coccinelle
script below. However, this doesn't handle comments, leaving references
to ACCESS_ONCE() instances which have been removed. As a preparatory
step, this patch converts the dcache code and comments to use
{READ,WRITE}_ONCE() consistently.
----
virtual patch
@ depends on patch @
expression E1, E2;
@@
- ACCESS_ONCE(E1) = E2
+ WRITE_ONCE(E1, E2)
@ depends on patch @
expression E;
@@
- ACCESS_ONCE(E)
+ READ_ONCE(E)
----
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: davem@davemloft.net
Cc: linux-arch@vger.kernel.org
Cc: mpe@ellerman.id.au
Cc: shuah@kernel.org
Cc: snitzer@redhat.com
Cc: thor.thayer@linux.intel.com
Cc: tj@kernel.org
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1508792849-3115-4-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
READ_ONCE() now has an implicit smp_read_barrier_depends() call, so it
can be used instead of lockless_dereference() without any change in
semantics.
Signed-off-by: Will Deacon <will.deacon@arm.com>
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>
Link: http://lkml.kernel.org/r/1508840570-22169-4-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull ->s_options removal from Al Viro:
"Preparations for fsmount/fsopen stuff (coming next cycle). Everything
gets moved to explicit ->show_options(), killing ->s_options off +
some cosmetic bits around fs/namespace.c and friends. Basically, the
stuff needed to work with fsmount series with minimum of conflicts
with other work.
It's not strictly required for this merge window, but it would reduce
the PITA during the coming cycle, so it would be nice to have those
bits and pieces out of the way"
* 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
isofs: Fix isofs_show_options()
VFS: Kill off s_options and helpers
orangefs: Implement show_options
9p: Implement show_options
isofs: Implement show_options
afs: Implement show_options
affs: Implement show_options
befs: Implement show_options
spufs: Implement show_options
bpf: Implement show_options
ramfs: Implement show_options
pstore: Implement show_options
omfs: Implement show_options
hugetlbfs: Implement show_options
VFS: Don't use save/replace_mount_options if not using generic_show_options
VFS: Provide empty name qstr
VFS: Make get_filesystem() return the affected filesystem
VFS: Clean up whitespace in fs/namespace.c and fs/super.c
Provide a function to create a NUL-terminated string from unterminated data
__list_lru_walk_one() acquires nlru spin lock (nlru->lock) for longer
duration if there are more number of items in the lru list. As per the
current code, it can hold the spin lock for upto maximum UINT_MAX
entries at a time. So if there are more number of items in the lru
list, then "BUG: spinlock lockup suspected" is observed in the below
path:
spin_bug+0x90
do_raw_spin_lock+0xfc
_raw_spin_lock+0x28
list_lru_add+0x28
dput+0x1c8
path_put+0x20
terminate_walk+0x3c
path_lookupat+0x100
filename_lookup+0x6c
user_path_at_empty+0x54
SyS_faccessat+0xd0
el0_svc_naked+0x24
This nlru->lock is acquired by another CPU in this path -
d_lru_shrink_move+0x34
dentry_lru_isolate_shrink+0x48
__list_lru_walk_one.isra.10+0x94
list_lru_walk_node+0x40
shrink_dcache_sb+0x60
do_remount_sb+0xbc
do_emergency_remount+0xb0
process_one_work+0x228
worker_thread+0x2e0
kthread+0xf4
ret_from_fork+0x10
Fix this lockup by reducing the number of entries to be shrinked from
the lru list to 1024 at once. Also, add cond_resched() before
processing the lru list again.
Link: http://marc.info/?t=149722864900001&r=1&w=2
Link: http://lkml.kernel.org/r/1498707575-2472-1-git-send-email-stummala@codeaurora.org
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
Suggested-by: Jan Kara <jack@suse.cz>
Suggested-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Alexander Polakov <apolyakov@beget.ru>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull misc filesystem updates from Al Viro:
"Assorted normal VFS / filesystems stuff..."
* 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
dentry name snapshots
Make statfs properly return read-only state after emergency remount
fs/dcache: init in_lookup_hashtable
minix: Deinline get_block, save 2691 bytes
fs: Reorder inode_owner_or_capable() to avoid needless
fs: warn in case userspace lied about modprobe return
take_dentry_name_snapshot() takes a safe snapshot of dentry name;
if the name is a short one, it gets copied into caller-supplied
structure, otherwise an extra reference to external name is grabbed
(those are never modified). In either case the pointer to stable
string is stored into the same structure.
dentry must be held by the caller of take_dentry_name_snapshot(),
but may be freely dropped afterwards - the snapshot will stay
until destroyed by release_dentry_name_snapshot().
Intended use:
struct name_snapshot s;
take_dentry_name_snapshot(&s, dentry);
...
access s.name
...
release_dentry_name_snapshot(&s);
Replaces fsnotify_oldname_...(), gets used in fsnotify to obtain the name
to pass down with event.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Provide an empty name (ie. "") qstr for general use.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
in_lookup_hashtable was introduced in commit 94bdd655ca ("parallel
lookups machinery, part 3") and never initialized but since it is in
the data it is all zeros. But we need this for -RT.
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
It's not hard to trigger a bunch of d_invalidate() on the same
dentry in parallel. They end up fighting each other - any
dentry picked for removal by one will be skipped by the rest
and we'll go for the next iteration through the entire
subtree, even if everything is being skipped. Morevoer, we
immediately go back to scanning the subtree. The only thing
we really need is to dissolve all mounts in the subtree and
as soon as we've nothing left to do, we can just unhash the
dentry and bugger off.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
By default we set DCACHE_REFERENCED and I_REFERENCED on any dentry or
inode we create. This is problematic as this means that it takes two
trips through the LRU for any of these objects to be reclaimed,
regardless of their actual lifetime. With enough pressure from these
caches we can easily evict our working set from page cache with single
use objects. So instead only set *REFERENCED if we've already been
added to the LRU list. This means that we've been touched since the
first time we were accessed, and so more likely to need to hang out in
cache.
To illustrate this issue I wrote the following scripts
https://github.com/josefbacik/debug-scripts/tree/master/cache-pressure
on my test box. It is a single socket 4 core CPU with 16gib of RAM and
I tested on an Intel 2tib NVME drive. The cache-pressure.sh script
creates a new file system and creates 2 6.5gib files in order to take up
13gib of the 16gib of ram with pagecache. Then it runs a test program
that reads these 2 files in a loop, and keeps track of how often it has
to read bytes for each loop. On an ideal system with no pressure we
should have to read 0 bytes indefinitely. The second thing this script
does is start a fs_mark job that creates a ton of 0 length files,
putting pressure on the system with slab only allocations. On exit the
script prints out how many bytes were read by the read-file program.
The results are as follows
Without patch:
/mnt/btrfs-test/reads/file1: total read during loops 27262988288
/mnt/btrfs-test/reads/file2: total read during loops 27262976000
With patch:
/mnt/btrfs-test/reads/file2: total read during loops 18640457728
/mnt/btrfs-test/reads/file1: total read during loops 9565376512
This patch results in a 50% reduction of the amount of pages evicted
from our working set.
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Protecting the mountpoint hashtable with namespace_sem was sufficient
until a call to umount_mnt was added to mntput_no_expire. At which
point it became possible for multiple calls of put_mountpoint on
the same hash chain to happen on the same time.
Kristen Johansen <kjlx@templeofstupid.com> reported:
> This can cause a panic when simultaneous callers of put_mountpoint
> attempt to free the same mountpoint. This occurs because some callers
> hold the mount_hash_lock, while others hold the namespace lock. Some
> even hold both.
>
> In this submitter's case, the panic manifested itself as a GP fault in
> put_mountpoint() when it called hlist_del() and attempted to dereference
> a m_hash.pprev that had been poisioned by another thread.
Al Viro observed that the simple fix is to switch from using the namespace_sem
to the mount_lock to protect the mountpoint hash table.
I have taken Al's suggested patch moved put_mountpoint in pivot_root
(instead of taking mount_lock an additional time), and have replaced
new_mountpoint with get_mountpoint a function that does the hash table
lookup and addition under the mount_lock. The introduction of get_mounptoint
ensures that only the mount_lock is needed to manipulate the mountpoint
hashtable.
d_set_mounted is modified to only set DCACHE_MOUNTED if it is not
already set. This allows get_mountpoint to use the setting of
DCACHE_MOUNTED to ensure adding a struct mountpoint for a dentry
happens exactly once.
Cc: stable@vger.kernel.org
Fixes: ce07d891a0 ("mnt: Honor MNT_LOCKED when detaching mounts")
Reported-by: Krister Johansen <kjlx@templeofstupid.com>
Suggested-by: Al Viro <viro@ZenIV.linux.org.uk>
Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This was entirely automated, using the script by Al:
PATT='^[[:blank:]]*#[[:blank:]]*include[[:blank:]]*<asm/uaccess.h>'
sed -i -e "s!$PATT!#include <linux/uaccess.h>!" \
$(git grep -l "$PATT"|grep -v ^include/linux/uaccess.h)
to do the replacement at the end of the merge window.
Requested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Now that path_has_submounts() has been added have_submounts() is no
longer used so remove it.
Link: http://lkml.kernel.org/r/20161011053428.27645.12310.stgit@pluto.themaw.net
Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
d_mountpoint() can only be used reliably to establish if a dentry is
not mounted in any namespace. It isn't aware of the possibility there
may be multiple mounts using the given dentry, possibly in a different
namespace.
Add function, path_has_submounts(), that checks is a struct path contains
mounts (or is a mountpoint itself) to handle this case.
Link: http://lkml.kernel.org/r/20161011053403.27645.55242.stgit@pluto.themaw.net
Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Pull more vfs updates from Al Viro:
"Assorted cleanups and fixes.
In the "trivial API change" department - ->d_compare() losing 'parent'
argument"
* 'for-linus-2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
cachefiles: Fix race between inactivating and culling a cache object
9p: use clone_fid()
9p: fix braino introduced in "9p: new helper - v9fs_parent_fid()"
vfs: make dentry_needs_remove_privs() internal
vfs: remove file_needs_remove_privs()
vfs: fix deadlock in file_remove_privs() on overlayfs
get rid of 'parent' argument of ->d_compare()
cifs, msdos, vfat, hfs+: don't bother with parent in ->d_compare()
affs ->d_compare(): don't bother with ->d_inode
fold _d_rehash() and __d_rehash() together
fold dentry_rcuwalk_invalidate() into its only remaining caller
Pull qstr constification updates from Al Viro:
"Fairly self-contained bunch - surprising lot of places passes struct
qstr * as an argument when const struct qstr * would suffice; it
complicates analysis for no good reason.
I'd prefer to feed that separately from the assorted fixes (those are
in #for-linus and with somewhat trickier topology)"
* 'work.const-qstr' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
qstr: constify instances in adfs
qstr: constify instances in lustre
qstr: constify instances in f2fs
qstr: constify instances in ext2
qstr: constify instances in vfat
qstr: constify instances in procfs
qstr: constify instances in fuse
qstr constify instances in fs/dcache.c
qstr: constify instances in nfs
qstr: constify instances in ocfs2
qstr: constify instances in autofs4
qstr: constify instances in hfs
qstr: constify instances in hfsplus
qstr: constify instances in logfs
qstr: constify dentry_init_security
The only place where we feed to __d_rehash() something other than
d_hash(dentry->d_name.hash) is __d_move(), where we give it d_hash
of another dentry. Postpone rehashing until we'd switched the
names and we are rid of that exception, along with the need to
keep _d_rehash() and __d_rehash() separate.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Pull vfs updates from Al Viro:
"Assorted cleanups and fixes.
Probably the most interesting part long-term is ->d_init() - that will
have a bunch of followups in (at least) ceph and lustre, but we'll
need to sort the barrier-related rules before it can get used for
really non-trivial stuff.
Another fun thing is the merge of ->d_iput() callers (dentry_iput()
and dentry_unlink_inode()) and a bunch of ->d_compare() ones (all
except the one in __d_lookup_lru())"
* 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (26 commits)
fs/dcache.c: avoid soft-lockup in dput()
vfs: new d_init method
vfs: Update lookup_dcache() comment
bdev: get rid of ->bd_inodes
Remove last traces of ->sync_page
new helper: d_same_name()
dentry_cmp(): use lockless_dereference() instead of smp_read_barrier_depends()
vfs: clean up documentation
vfs: document ->d_real()
vfs: merge .d_select_inode() into .d_real()
unify dentry_iput() and dentry_unlink_inode()
binfmt_misc: ->s_root is not going anywhere
drop redundant ->owner initializations
ufs: get rid of redundant checks
orangefs: constify inode_operations
missed comment updates from ->direct_IO() prototype change
file_inode(f)->i_mapping is f->f_mapping
trim fsnotify hooks a bit
9p: new helper - v9fs_parent_fid()
debugfs: ->d_parent is never NULL or negative
...
This changes the vfs dentry hashing to mix in the parent pointer at the
_beginning_ of the hash, rather than at the end.
That actually improves both the hash and the code generation, because we
can move more of the computation to the "static" part of the dcache
setup, and do less at lookup runtime.
It turns out that a lot of other hash users also really wanted to mix in
a base pointer as a 'salt' for the hash, and so the slightly extended
interface ends up working well for other cases too.
Users that want a string hash that is purely about the string pass in a
'salt' pointer of NULL.
* merge branch 'salted-string-hash':
fs/dcache.c: Save one 32-bit multiply in dcache lookup
vfs: make the string hashes salt the hash
We triggered soft-lockup under stress test which
open/access/write/close one file concurrently on more than
five different CPUs:
WARN: soft lockup - CPU#0 stuck for 11s! [who:30631]
...
[<ffffffc0003986f8>] dput+0x100/0x298
[<ffffffc00038c2dc>] terminate_walk+0x4c/0x60
[<ffffffc00038f56c>] path_lookupat+0x5cc/0x7a8
[<ffffffc00038f780>] filename_lookup+0x38/0xf0
[<ffffffc000391180>] user_path_at_empty+0x78/0xd0
[<ffffffc0003911f4>] user_path_at+0x1c/0x28
[<ffffffc00037d4fc>] SyS_faccessat+0xb4/0x230
->d_lock trylock may failed many times because of concurrently
operations, and dput() may execute a long time.
Fix this by replacing cpu_relax() with cond_resched().
dput() used to be sleepable, so make it sleepable again
should be safe.
Cc: <stable@vger.kernel.org>
Signed-off-by: Wei Fang <fangwei1@huawei.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
lockless_dereference() was added which can be used in place of
hard-coding smp_read_barrier_depends().
Signed-off-by: He Kuang <hekuang@huawei.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
The two methods essentially do the same: find the real dentry/inode
belonging to an overlay dentry. The difference is in the usage:
vfs_open() uses ->d_select_inode() and expects the function to perform
copy-up if necessary based on the open flags argument.
file_dentry() uses ->d_real() passing in the overlay dentry as well as the
underlying inode.
vfs_rename() uses ->d_select_inode() but passes zero flags. ->d_real()
with a zero inode would have worked just as well here.
This patch merges the functionality of ->d_select_inode() into ->d_real()
by adding an 'open_flags' argument to the latter.
[Al Viro] Make the signature of d_real() match that of ->d_real() again.
And constify the inode argument, while we are at it.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Check for d_unhashed() while searching in in-lookup hash was absolutely
wrong. Worse, it masked a deadlock on dget() done under bitlock that
nests inside ->d_lock. Thanks to J. R. Okajima for spotting it.
Spotted-by: "J. R. Okajima" <hooanon05g@gmail.com>
Wearing-brown-paperbag: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Noe that we're mixing in the parent pointer earlier, we
don't need to use hash_32() to mix its bits. Instead, we can
just take the msbits of the hash value directly.
For those applications which use the partial_name_hash(),
move the multiply to end_name_hash.
Signed-off-by: George Spelvin <linux@sciencehorizons.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We always mixed in the parent pointer into the dentry name hash, but we
did it late at lookup time. It turns out that we can simplify that
lookup-time action by salting the hash with the parent pointer early
instead of late.
A few other users of our string hashes also wanted to mix in their own
pointers into the hash, and those are updated to use the same mechanism.
Hash users that don't have any particular initial salt can just use the
NULL pointer as a no-salt.
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: George Spelvin <linux@sciencehorizons.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
d_walk() relies upon the tree not getting rearranged under it without
rename_lock being touched. And we do grab rename_lock around the
places that change the tree topology. Unfortunately, branch reordering
is just as bad from d_walk() POV and we have two places that do it
without touching rename_lock - one in handling of cursors (for ramfs-style
directories) and another in autofs. autofs one is a separate story; this
commit deals with the cursors.
* mark cursor dentries explicitly at allocation time
* make __dentry_kill() leave ->d_child.next pointing to the next
non-cursor sibling, making sure that it won't be moved around unnoticed
before the parent is relocked on ascend-to-parent path in d_walk().
* make d_walk() skip cursors explicitly; strictly speaking it's
not necessary (all callbacks we pass to d_walk() are no-ops on cursors),
but it makes analysis easier.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Ascend-to-parent logics in d_walk() depends on all encountered child
dentries not getting freed without an RCU delay. Unfortunately, in
quite a few cases it is not true, with hard-to-hit oopsable race as
the result.
Fortunately, the fix is simiple; right now the rule is "if it ever
been hashed, freeing must be delayed" and changing it to "if it
ever had a parent, freeing must be delayed" closes that hole and
covers all cases the old rule used to cover. Moreover, pipes and
sockets remain _not_ covered, so we do not introduce RCU delay in
the cases which are the reason for having that delay conditional
in the first place.
Cc: stable@vger.kernel.org # v3.2+ (and watch out for __d_materialise_dentry())
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
There is a lot of duplication between dentry_unlink_inode() and dentry_iput().
The only real difference is that dentry_unlink_inode() bumps ->d_seq and
dentry_iput() doesn't. The argument of the latter is known to have been
unhashed, so anybody who might've found it in RCU lookup would already be
doomed to a ->d_seq mismatch. And we want to avoid pointless smp_rmb() there.
This patch makes dentry_unlink_inode() bump ->d_seq only for hashed dentries.
It's safe (d_delete() calls that sucker only if we are holding the only
reference to dentry, so rehash is not going to happen) and it allows
to use dentry_unlink_inode() in __dentry_kill() and get rid of dentry_iput().
The interesting question here is profiling; it *is* a hot path, and extra
conditional jumps in there might or might not be painful.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
fsnotify_d_move()/__fsnotify_d_instantiate()/__fsnotify_update_dcache_flags()
are identical to each other, regardless of the config.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Pull string hash improvements from George Spelvin:
"This series does several related things:
- Makes the dcache hash (fs/namei.c) useful for general kernel use.
(Thanks to Bruce for noticing the zero-length corner case)
- Converts the string hashes in <linux/sunrpc/svcauth.h> to use the
above.
- Avoids 64-bit multiplies in hash_64() on 32-bit platforms. Two
32-bit multiplies will do well enough.
- Rids the world of the bad hash multipliers in hash_32.
This finishes the job started in commit 689de1d6ca ("Minimal
fix-up of bad hashing behavior of hash_64()")
The vast majority of Linux architectures have hardware support for
32x32-bit multiply and so derive no benefit from "simplified"
multipliers.
The few processors that do not (68000, h8/300 and some models of
Microblaze) have arch-specific implementations added. Those
patches are last in the series.
- Overhauls the dcache hash mixing.
The patch in commit 0fed3ac866 ("namei: Improve hash mixing if
CONFIG_DCACHE_WORD_ACCESS") was an off-the-cuff suggestion.
Replaced with a much more careful design that's simultaneously
faster and better. (My own invention, as there was noting suitable
in the literature I could find. Comments welcome!)
- Modify the hash_name() loop to skip the initial HASH_MIX(). This
would let us salt the hash if we ever wanted to.
- Sort out partial_name_hash().
The hash function is declared as using a long state, even though
it's truncated to 32 bits at the end and the extra internal state
contributes nothing to the result. And some callers do odd things:
- fs/hfs/string.c only allocates 32 bits of state
- fs/hfsplus/unicode.c uses it to hash 16-bit unicode symbols not bytes
- Modify bytemask_from_count to handle inputs of 1..sizeof(long)
rather than 0..sizeof(long)-1. This would simplify users other
than full_name_hash"
Special thanks to Bruce Fields for testing and finding bugs in v1. (I
learned some humbling lessons about "obviously correct" code.)
On the arch-specific front, the m68k assembly has been tested in a
standalone test harness, I've been in contact with the Microblaze
maintainers who mostly don't care, as the hardware multiplier is never
omitted in real-world applications, and I haven't heard anything from
the H8/300 world"
* 'hash' of git://ftp.sciencehorizons.net/linux:
h8300: Add <asm/hash.h>
microblaze: Add <asm/hash.h>
m68k: Add <asm/hash.h>
<linux/hash.h>: Add support for architecture-specific functions
fs/namei.c: Improve dcache hash function
Eliminate bad hash multipliers from hash_32() and hash_64()
Change hash_64() return value to 32 bits
<linux/sunrpc/svcauth.h>: Define hash_str() in terms of hashlen_string()
fs/namei.c: Add hashlen_string() function
Pull out string hash to <linux/stringhash.h>
We'd like to make more use of the highly-optimized dcache hash functions
throughout the kernel, rather than have every subsystem create its own,
and a function that hashes basic null-terminated strings is required
for that.
(The name is to emphasize that it returns both hash and length.)
It's actually useful in the dcache itself, specifically d_alloc_name().
Other uses in the next patch.
full_name_hash() is also tweaked to make it more generally useful:
1) Take a "char *" rather than "unsigned char *" argument, to
be consistent with hash_name().
2) Handle zero-length inputs. If we want more callers, we don't want
to make them worry about corner cases.
Signed-off-by: George Spelvin <linux@sciencehorizons.net>
Pull misc vfs cleanups from Al Viro:
"Assorted cleanups and fixes all over the place"
* 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
coredump: only charge written data against RLIMIT_CORE
coredump: get rid of coredump_params->written
ecryptfs_lookup(): try either only encrypted or plaintext name
ecryptfs: avoid multiple aliases for directories
bpf: reject invalid names right in ->lookup()
__d_alloc(): treat NULL name as QSTR("/", 1)
mtd: switch ubi_open_volume_path() to vfs_stat()
mtd: switch open_mtd_by_chdev() to use of vfs_stat()
ta-da!
The main issue is the lack of down_write_killable(), so the places
like readdir.c switched to plain inode_lock(); once killable
variants of rwsem primitives appear, that'll be dealt with.
lockdep side also might need more work
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
If we *do* run into an in-lookup match, we need to wait for it to
cease being in-lookup. Fortunately, we do have unused space in
in-lookup dentries - d_lru is never looked at until it stops being
in-lookup.
So we can stash a pointer to wait_queue_head from stack frame of
the caller of ->lookup(). Some precautions are needed while
waiting, but it's not that hard - we do hold a reference to dentry
we are waiting for, so it can't go away. If it's found to be
in-lookup the wait_queue_head is still alive and will remain so
at least while ->d_lock is held. Moreover, the condition we
are waiting for becomes true at the same point where everything
on that wq gets woken up, so we can just add ourselves to the
queue once.
d_alloc_parallel() gets a pointer to wait_queue_head_t from its
caller; lookup_slow() adjusted, d_add_ci() taught to use
d_alloc_parallel() if the dentry passed to it happens to be
in-lookup one (i.e. if it's been called from the parallel lookup).
That's pretty much it - all that remains is to switch ->i_mutex
to rwsem and have lookup_slow() take it shared.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
We will need to be able to check if there is an in-lookup
dentry with matching parent/name. Right now it's impossible,
but as soon as start locking directories shared such beasts
will appear.
Add a secondary hash for locating those. Hash chains go through
the same space where d_alias will be once it's not in-lookup anymore.
Search is done under the same bitlock we use for modifications -
with the primary hash we can rely on d_rehash() into the wrong
chain being the worst that could happen, but here the pointers are
buggered once it's removed from the chain. On the other hand,
the chains are not going to be long and normally we'll end up
adding to the chain anyway. That allows us to avoid bothering with
->d_lock when doing the comparisons - everything is stable until
removed from chain.
New helper: d_alloc_parallel(). Right now it allocates, verifies
that no hashed and in-lookup matches exist and adds to in-lookup
hash.
Returns ERR_PTR() for error, hashed match (in the unlikely case it's
been found) or new dentry. In-lookup matches trigger BUG() for
now; that will change in the next commit when we introduce waiting
for ongoing lookup to finish. Note that in-lookup matches won't be
possible until we actually go for shared locking.
lookup_slow() switched to use of d_alloc_parallel().
Again, these commits are separated only for making it easier to
review. All this machinery will start doing something useful only
when we go for shared locking; it's just that the combination is
too large for my taste.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
We'll need to verify that there's neither a hashed nor in-lookup
dentry with desired parent/name before adding to in-lookup set.
One possible solution would be to hold the parent's ->d_lock through
both checks, but while the in-lookup set is relatively small at any
time, dcache is not. And holding the parent's ->d_lock through
something like __d_lookup_rcu() would suck too badly.
So we leave the parent's ->d_lock alone, which means that we watch
out for the following scenario:
* we verify that there's no hashed match
* existing in-lookup match gets hashed by another process
* we verify that there's no in-lookup matches and decide
that everything's fine.
Solution: per-directory kinda-sorta seqlock, bumped around the times
we hash something that used to be in-lookup or move (and hash)
something in place of in-lookup. Then the above would turn into
* read the counter
* do dcache lookup
* if no matches found, check for in-lookup matches
* if there had been none of those either, check if the
counter has changed; repeat if it has.
The "kinda-sorta" part is due to the fact that we don't have much spare
space in inode. There is a spare word (shared with i_bdev/i_cdev/i_pipe),
so the counter part is not a problem, but spinlock is a different story.
We could use the parent's ->d_lock, and it would be less painful in
terms of contention, for __d_add() it would be rather inconvenient to
grab; we could do that (using lock_parent()), but...
Fortunately, we can get serialization on the counter itself, and it
might be a good idea in general; we can use cmpxchg() in a loop to
get from even to odd and smp_store_release() from odd to even.
This commit adds the counter and updating logics; the readers will be
added in the next commit.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
marked as such when (would be) parallel lookup is about to pass them
to actual ->lookup(); unmarked when
* __d_add() is about to make it hashed, positive or not.
* __d_move() (from d_splice_alias(), directly or via
__d_unalias()) puts a preexisting dentry in its place
* in caller of ->lookup() if it has escaped all of the
above. Bug (WARN_ON, actually) if it reaches the final dput()
or d_instantiate() while still marked such.
As the result, we are guaranteed that for as long as the flag is
set, dentry will
* remain negative unhashed with positive refcount
* never have its ->d_alias looked at
* never have its ->d_lru looked at
* never have its ->d_parent and ->d_name changed
Right now we have at most one such for any given parent directory.
With parallel lookups that restriction will weaken to
* only exist when parent is locked shared
* at most one with given (parent,name) pair (comparison of
names is according to ->d_compare())
* only exist when there's no hashed dentry with the same
(parent,name)
Transition will take the next several commits; unfortunately, we'll
only be able to switch to rwsem at the end of this series. The
reason for not making it a single patch is to simplify review.
New primitives: d_in_lookup() (a predicate checking if dentry is in
the in-lookup state) and d_lookup_done() (tells the system that
we are done with lookup and if it's still marked as in-lookup, it
should cease to be such).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This series fixes bugs in nfs and ext4 due to 4bacc9c923 ("overlayfs:
Make f_path always point to the overlay and f_inode to the underlay").
Regular files opened on overlayfs will result in the file being opened on
the underlying filesystem, while f_path points to the overlayfs
mount/dentry.
This confuses filesystems which get the dentry from struct file and assume
it's theirs.
Add a new helper, file_dentry() [*], to get the filesystem's own dentry
from the file. This checks file->f_path.dentry->d_flags against
DCACHE_OP_REAL, and returns file->f_path.dentry if DCACHE_OP_REAL is not
set (this is the common, non-overlayfs case).
In the uncommon case it will call into overlayfs's ->d_real() to get the
underlying dentry, matching file_inode(file).
The reason we need to check against the inode is that if the file is copied
up while being open, d_real() would return the upper dentry, while the open
file comes from the lower dentry.
[*] If possible, it's better simply to use file_inode() instead.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Tested-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: <stable@vger.kernel.org> # v4.2
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Daniel Axtens <dja@axtens.net>
d_add() with inode->i_lock already held; common to d_add() and
d_splice_alias(). All ->lookup() instances that end up hashing
the dentry they are given will hash it here.
This almost completes the preparations to parallel lookups
proper - the only remaining bit is taking security_d_instantiate()
past d_rehash() and doing rehashing without dropping ->d_lock.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
First of all, don't bother calling it if inode is NULL -
that makes inode argument unused. Moreover, do it *before*
dropping ->d_lock, not right after that (and don't bother
grabbing ->d_lock in it, of course).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
new primitive: d_exact_alias(dentry, inode). If there is an unhashed
dentry with the same name/parent and given inode, rehash, grab and
return it. Otherwise, return NULL. The only caller of d_add_unique()
switched to d_exact_alias() + d_splice_alias().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Games with ordering and barriers are way too brittle. Just
bump ->d_seq before and after updating ->d_inode and ->d_flags
type bits, so that verifying ->d_seq would guarantee they are
coherent.
Cc: stable@vger.kernel.org # v3.13+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
parallel to mutex_{lock,unlock,trylock,is_locked,lock_nested},
inode_foo(inode) being mutex_foo(&inode->i_mutex).
Please, use those for access to ->i_mutex; over the coming cycle
->i_mutex will become rwsem, with ->lookup() done with it held
only shared.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Mark those kmem allocations that are known to be easily triggered from
userspace as __GFP_ACCOUNT/SLAB_ACCOUNT, which makes them accounted to
memcg. For the list, see below:
- threadinfo
- task_struct
- task_delay_info
- pid
- cred
- mm_struct
- vm_area_struct and vm_region (nommu)
- anon_vma and anon_vma_chain
- signal_struct
- sighand_struct
- fs_struct
- files_struct
- fdtable and fdtable->full_fds_bits
- dentry and external_name
- inode for all filesystems. This is the most tedious part, because
most filesystems overwrite the alloc_inode method.
The list is far from complete, so feel free to add more objects.
Nevertheless, it should be close to "account everything" approach and
keep most workloads within bounds. Malevolent users will be able to
breach the limit, but this was possible even with the former "account
everything" approach (simply because it did not account everything in
fact).
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Greg Thelen <gthelen@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull misc vfs updates from Al Viro:
"All kinds of stuff. That probably should've been 5 or 6 separate
branches, but by the time I'd realized how large and mixed that bag
had become it had been too close to -final to play with rebasing.
Some fs/namei.c cleanups there, memdup_user_nul() introduction and
switching open-coded instances, burying long-dead code, whack-a-mole
of various kinds, several new helpers for ->llseek(), assorted
cleanups and fixes from various people, etc.
One piece probably deserves special mention - Neil's
lookup_one_len_unlocked(). Similar to lookup_one_len(), but gets
called without ->i_mutex and tries to avoid ever taking it. That, of
course, means that it's not useful for any directory modifications,
but things like getting inode attributes in nfds readdirplus are fine
with that. I really should've asked for moratorium on lookup-related
changes this cycle, but since I hadn't done that early enough... I
*am* asking for that for the coming cycle, though - I'm going to try
and get conversion of i_mutex to rwsem with ->lookup() done under lock
taken shared.
There will be a patch closer to the end of the window, along the lines
of the one Linus had posted last May - mechanical conversion of
->i_mutex accesses to inode_lock()/inode_unlock()/inode_trylock()/
inode_is_locked()/inode_lock_nested(). To quote Linus back then:
-----
| This is an automated patch using
|
| sed 's/mutex_lock(&\(.*\)->i_mutex)/inode_lock(\1)/'
| sed 's/mutex_unlock(&\(.*\)->i_mutex)/inode_unlock(\1)/'
| sed 's/mutex_lock_nested(&\(.*\)->i_mutex,[ ]*I_MUTEX_\([A-Z0-9_]*\))/inode_lock_nested(\1, I_MUTEX_\2)/'
| sed 's/mutex_is_locked(&\(.*\)->i_mutex)/inode_is_locked(\1)/'
| sed 's/mutex_trylock(&\(.*\)->i_mutex)/inode_trylock(\1)/'
|
| with a very few manual fixups
-----
I'm going to send that once the ->i_mutex-affecting stuff in -next
gets mostly merged (or when Linus says he's about to stop taking
merges)"
* 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (63 commits)
nfsd: don't hold i_mutex over userspace upcalls
fs:affs:Replace time_t with time64_t
fs/9p: use fscache mutex rather than spinlock
proc: add a reschedule point in proc_readfd_common()
logfs: constify logfs_block_ops structures
fcntl: allow to set O_DIRECT flag on pipe
fs: __generic_file_splice_read retry lookup on AOP_TRUNCATED_PAGE
fs: xattr: Use kvfree()
[s390] page_to_phys() always returns a multiple of PAGE_SIZE
nbd: use ->compat_ioctl()
fs: use block_device name vsprintf helper
lib/vsprintf: add %*pg format specifier
fs: use gendisk->disk_name where possible
poll: plug an unused argument to do_poll
amdkfd: don't open-code memdup_user()
cdrom: don't open-code memdup_user()
rsxx: don't open-code memdup_user()
mtip32xx: don't open-code memdup_user()
[um] mconsole: don't open-code memdup_user_nul()
[um] hostaudio: don't open-code memdup_user()
...
new method: ->get_link(); replacement of ->follow_link(). The differences
are:
* inode and dentry are passed separately
* might be called both in RCU and non-RCU mode;
the former is indicated by passing it a NULL dentry.
* when called that way it isn't allowed to block
and should return ERR_PTR(-ECHILD) if it needs to be called
in non-RCU mode.
It's a flagday change - the old method is gone, all in-tree instances
converted. Conversion isn't hard; said that, so far very few instances
do not immediately bail out when called in RCU mode. That'll change
in the next commits.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This patch makes is_subdir return bool to improve
readability due to this particular function only using either
one or zero as its return value.
No functional change.
Signed-off-by: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
i_lock is only needed until __d_find_any_alias calls dget on the alias
dentry. After that the reference to new ensures that dentry_kill and
d_delete will not remove the inode from the dentry, and remove the
dentry from the inode->d_entry list.
The inode i_lock came to be held over the the __d_move calls in
d_splice_alias through a series of introduction of locks with
increasing smaller scope. First it was the dcache_lock, then
it was the dcache_inode_lock, and finally inode->i_lock.
Furthermore inode->i_lock is not held over any other calls
to d_move or __d_move so it can not provide any meaningful
rename protection.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
A rename can result in a dentry that by walking up d_parent
will never reach it's mnt_root. For lack of a better term
I call this an escaped path.
prepend_path is called by four different functions __d_path,
d_absolute_path, d_path, and getcwd.
__d_path only wants to see paths are connected to the root it passes
in. So __d_path needs prepend_path to return an error.
d_absolute_path similarly wants to see paths that are connected to
some root. Escaped paths are not connected to any mnt_root so
d_absolute_path needs prepend_path to return an error greater
than 1. So escaped paths will be treated like paths on lazily
unmounted mounts.
getcwd needs to prepend "(unreachable)" so getcwd also needs
prepend_path to return an error.
d_path is the interesting hold out. d_path just wants to print
something, and does not care about the weird cases. Which raises
the question what should be printed?
Given that <escaped_path>/<anything> should result in -ENOENT I
believe it is desirable for escaped paths to be printed as empty
paths. As there are not really any meaninful path components when
considered from the perspective of a mount tree.
So tweak prepend_path to return an empty path with an new error
code of 3 when it encounters an escaped path.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Dave Hansen reported the following;
My laptop has been behaving strangely with 4.2-rc2. Once I log
in to my X session, I start getting all kinds of strange errors
from applications and see this in my dmesg:
VFS: file-max limit 8192 reached
The problem is that the file-max is calculated before memory is fully
initialised and miscalculates how much memory the kernel is using. This
patch recalculates file-max after deferred memory initialisation. Note
that using memory hotplug infrastructure would not have avoided this
problem as the value is not recalculated after memory hot-add.
4.1: files_stat.max_files = 6582781
4.2-rc2: files_stat.max_files = 8192
4.2-rc2 patched: files_stat.max_files = 6562467
Small differences with the patch applied and 4.1 but not enough to matter.
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reported-by: Dave Hansen <dave.hansen@intel.com>
Cc: Nicolai Stange <nicstange@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Alex Ng <alexng@microsoft.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Al Viro
John Ogness
Will Deacon
Linus Torvalds
Andrey Ryabinin
Alexey Dobriyan
Miklos Szeredi
Amir Goldstein
David Windsor
NeilBrown
Yang Shi
Paul E. McKenney
Levin, Alexander (Sasha Levin)
Mark Rutland
Sahitya Tummala
Pavel Tatashin
David Howells
Sebastian Andrzej Siewior
Josef Bacik
Eric W. Biederman
Ian Kent
Wei Fang
Miklos Szeredi
He Kuang
George Spelvin
Vladimir Davydov
Yaowei Bai
Mel Gorman