dentries of created objects in dcache (and undo it when removing those).
Reference is grabbed and not released, but it's not actually _stored_
anywhere. That works, but it's hard to follow and verify; among other
things, we have no way to tell _which_ of the increments is intended
to be an unpaired one. Worse, on removal we need to decide whether
the reference had already been dropped, which can be non-trivial if
that removal is on umount and we need to figure out if this dentry is
pinned due to e.g. unlink() not done. Usually that is handled by using
kill_litter_super() as ->kill_sb(), but there are open-coded special
cases of the same (consider e.g. /proc/self).
Things get simpler if we introduce a new dentry flag (DCACHE_PERSISTENT)
marking those "leaked" dentries. Having it set claims responsibility
for +1 in refcount.
The end result this series is aiming for:
* get these unbalanced dget() and dput() replaced with new primitives that
would, in addition to adjusting refcount, set and clear persistency flag.
* instead of having kill_litter_super() mess with removing the remaining
"leaked" references (e.g. for all tmpfs files that hadn't been removed
prior to umount), have the regular shrink_dcache_for_umount() strip
DCACHE_PERSISTENT of all dentries, dropping the corresponding
reference if it had been set. After that kill_litter_super() becomes
an equivalent of kill_anon_super().
Doing that in a single step is not feasible - it would affect too many places
in too many filesystems. It has to be split into a series.
This work has really started early in 2024; quite a few preliminary pieces
have already gone into mainline. This chunk is finally getting to the
meat of that stuff - infrastructure and most of the conversions to it.
Some pieces are still sitting in the local branches, but the bulk of
that stuff is here.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Merge tag 'pull-persistency' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull persistent dentry infrastructure and conversion from Al Viro:
"Some filesystems use a kinda-sorta controlled dentry refcount leak to
pin dentries of created objects in dcache (and undo it when removing
those). A reference is grabbed and not released, but it's not actually
_stored_ anywhere.
That works, but it's hard to follow and verify; among other things, we
have no way to tell _which_ of the increments is intended to be an
unpaired one. Worse, on removal we need to decide whether the
reference had already been dropped, which can be non-trivial if that
removal is on umount and we need to figure out if this dentry is
pinned due to e.g. unlink() not done. Usually that is handled by using
kill_litter_super() as ->kill_sb(), but there are open-coded special
cases of the same (consider e.g. /proc/self).
Things get simpler if we introduce a new dentry flag
(DCACHE_PERSISTENT) marking those "leaked" dentries. Having it set
claims responsibility for +1 in refcount.
The end result this series is aiming for:
- get these unbalanced dget() and dput() replaced with new primitives
that would, in addition to adjusting refcount, set and clear
persistency flag.
- instead of having kill_litter_super() mess with removing the
remaining "leaked" references (e.g. for all tmpfs files that hadn't
been removed prior to umount), have the regular
shrink_dcache_for_umount() strip DCACHE_PERSISTENT of all dentries,
dropping the corresponding reference if it had been set. After that
kill_litter_super() becomes an equivalent of kill_anon_super().
Doing that in a single step is not feasible - it would affect too many
places in too many filesystems. It has to be split into a series.
This work has really started early in 2024; quite a few preliminary
pieces have already gone into mainline. This chunk is finally getting
to the meat of that stuff - infrastructure and most of the conversions
to it.
Some pieces are still sitting in the local branches, but the bulk of
that stuff is here"
* tag 'pull-persistency' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (54 commits)
d_make_discardable(): warn if given a non-persistent dentry
kill securityfs_recursive_remove()
convert securityfs
get rid of kill_litter_super()
convert rust_binderfs
convert nfsctl
convert rpc_pipefs
convert hypfs
hypfs: swich hypfs_create_u64() to returning int
hypfs: switch hypfs_create_str() to returning int
hypfs: don't pin dentries twice
convert gadgetfs
gadgetfs: switch to simple_remove_by_name()
convert functionfs
functionfs: switch to simple_remove_by_name()
functionfs: fix the open/removal races
functionfs: need to cancel ->reset_work in ->kill_sb()
functionfs: don't bother with ffs->ref in ffs_data_{opened,closed}()
functionfs: don't abuse ffs_data_closed() on fs shutdown
convert selinuxfs
...
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Merge tag 'vfs-6.19-rc1.inode' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull vfs inode updates from Christian Brauner:
"Features:
- Hide inode->i_state behind accessors. Open-coded accesses prevent
asserting they are done correctly. One obvious aspect is locking,
but significantly more can be checked. For example it can be
detected when the code is clearing flags which are already missing,
or is setting flags when it is illegal (e.g., I_FREEING when
->i_count > 0)
- Provide accessors for ->i_state, converts all filesystems using
coccinelle and manual conversions (btrfs, ceph, smb, f2fs, gfs2,
overlayfs, nilfs2, xfs), and makes plain ->i_state access fail to
compile
- Rework I_NEW handling to operate without fences, simplifying the
code after the accessor infrastructure is in place
Cleanups:
- Move wait_on_inode() from writeback.h to fs.h
- Spell out fenced ->i_state accesses with explicit smp_wmb/smp_rmb
for clarity
- Cosmetic fixes to LRU handling
- Push list presence check into inode_io_list_del()
- Touch up predicts in __d_lookup_rcu()
- ocfs2: retire ocfs2_drop_inode() and I_WILL_FREE usage
- Assert on ->i_count in iput_final()
- Assert ->i_lock held in __iget()
Fixes:
- Add missing fences to I_NEW handling"
* tag 'vfs-6.19-rc1.inode' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (22 commits)
dcache: touch up predicts in __d_lookup_rcu()
fs: push list presence check into inode_io_list_del()
fs: cosmetic fixes to lru handling
fs: rework I_NEW handling to operate without fences
fs: make plain ->i_state access fail to compile
xfs: use the new ->i_state accessors
nilfs2: use the new ->i_state accessors
overlayfs: use the new ->i_state accessors
gfs2: use the new ->i_state accessors
f2fs: use the new ->i_state accessors
smb: use the new ->i_state accessors
ceph: use the new ->i_state accessors
btrfs: use the new ->i_state accessors
Manual conversion to use ->i_state accessors of all places not covered by coccinelle
Coccinelle-based conversion to use ->i_state accessors
fs: provide accessors for ->i_state
fs: spell out fenced ->i_state accesses with explicit smp_wmb/smp_rmb
fs: move wait_on_inode() from writeback.h to fs.h
fs: add missing fences to I_NEW handling
ocfs2: retire ocfs2_drop_inode() and I_WILL_FREE usage
...
Rationale is that if the parent dentry is the same and the length is the
same, then you have to be unlucky for the name to not match.
At the same time the dentry was literally just found on the hash, so you
have to be even more unlucky to determine it is unhashed.
While here add commentary while d_unhashed() is necessary. It was
already removed once and brought back in:
2e321806b6 ("Revert "vfs: remove unnecessary d_unhashed() check from __d_lookup_rcu"")
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://patch.msgid.link/20251127131526.4137768-1-mjguzik@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
In the inode hash code grab the state while ->i_lock is held. If found
to be set, synchronize the sleep once more with the lock held.
In the real world the flag is not set most of the time.
Apart from being simpler to reason about, it comes with a minor speed up
as now clearing the flag does not require the smp_mb() fence.
While here rename wait_on_inode() to wait_on_new_inode() to line it up
with __wait_on_freeing_inode().
Christian Brauner <brauner@kernel.org> says:
As per the discussion in [1] I folded in the diff sent in [2].
Link: https://lore.kernel.org/69238e4d.a70a0220.d98e3.006e.GAE@google.com [1]
Link: https://lore.kernel.org/c2kpawomkbvtahjm7y5mposbhckb7wxthi3iqy5yr22ggpucrm@ufvxwy233qxo [2]
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://patch.msgid.link/20251010221737.1403539-1-mjguzik@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
At this point there are very few call chains that might lead to
d_make_discardable() on a dentry that hadn't been made persistent:
calls of simple_unlink() and simple_rmdir() in configfs and
apparmorfs.
Both filesystems do pin (part of) their contents in dcache, but
they are currently playing very unusual games with that. Converting
them to more usual patterns might be possible, but it's definitely
going to be a long series of changes in both cases.
For now the easiest solution is to have both stop using simple_unlink()
and simple_rmdir() - that allows to make d_make_discardable() warn
when given a non-persistent dentry.
Rather than giving them full-blown private copies (with calls of
d_make_discardable() replaced with dput()), let's pull the parts of
simple_unlink() and simple_rmdir() that deal with timestamps and link
counts into separate helpers (__simple_unlink() and __simple_rmdir()
resp.) and have those used by configfs and apparmorfs.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* d_make_persistent(dentry, inode) - bump refcount, mark persistent and
make hashed positive. Return value is a borrowed reference to dentry;
it can be used until something removes persistency (at the very least,
until the parent gets unlocked, but some filesystems may have stronger
exclusion).
* d_make_discardable() - remove persistency mark and drop reference.
d_make_persistent() is similar to combination of d_instantiate(), dget()
and setting flag. The only difference is that unlike d_instantiate()
it accepts hashed and unhashed negatives alike. It is always called in
strong locking environment (parent held exclusive, or, in some cases,
dentry coming from d_alloc_name()); if we ever start using it with parent
held only shared and dentry coming from d_alloc_parallel(), we'll need
to copy the in-lookup logics from __d_add().
d_make_discardable() is eqiuvalent to combination of removing flag and
dput(); since flag removal requires ->d_lock, there's no point trying
to avoid taking that for refcount decrement as fast_dput() does.
The slow path of dput() has been taken into a helper and reused in
d_make_discardable() instead.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Some filesystems use a kinda-sorta controlled dentry refcount leak to pin
dentries of created objects in dcache (and undo it when removing those).
Reference is grabbed and not released, but it's not actually _stored_
anywhere. That works, but it's hard to follow and verify; among other
things, we have no way to tell _which_ of the increments is intended
to be an unpaired one. Worse, on removal we need to decide whether
the reference had already been dropped, which can be non-trivial if
that removal is on umount and we need to figure out if this dentry is
pinned due to e.g. unlink() not done. Usually that is handled by using
kill_litter_super() as ->kill_sb(), but there are open-coded special
cases of the same (consider e.g. /proc/self).
Things get simpler if we introduce a new dentry flag (DCACHE_PERSISTENT)
marking those "leaked" dentries. Having it set claims responsibility
for +1 in refcount.
The end result this series is aiming for:
* get these unbalanced dget() and dput() replaced with new primitives that
would, in addition to adjusting refcount, set and clear persistency flag.
* instead of having kill_litter_super() mess with removing the remaining
"leaked" references (e.g. for all tmpfs files that hadn't been removed
prior to umount), have the regular shrink_dcache_for_umount() strip
DCACHE_PERSISTENT of all dentries, dropping the corresponding
reference if it had been set. After that kill_litter_super() becomes
an equivalent of kill_anon_super().
Doing that in a single step is not feasible - it would affect too many places
in too many filesystems. It has to be split into a series.
Here we
* introduce the new flag
* teach shrink_dcache_for_umount() to handle it (i.e. remove
and drop refcount on anything that survives to umount with that flag
still set)
* teach kill_litter_super() that anything with that flag does
*not* need to be unpinned.
Next commits will add primitives for maintaing that flag and convert the
common helpers to those. After that - a long series of per-filesystem
patches converting to those primitives.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Suppose there are 2 CPUs racing inode hash lookup func (say ilookup5())
and unlock_new_inode().
In principle the latter can clear the I_NEW flag before prior stores
into the inode were made visible.
The former can in turn observe I_NEW is cleared and proceed to use the
inode, while possibly reading from not-yet-published areas.
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
When user calls open_by_handle_at() on some inode that is not cached, we
will create disconnected dentry for it. If such dentry is a directory,
exportfs_decode_fh_raw() will then try to connect this dentry to the
dentry tree through reconnect_path(). It may happen for various reasons
(such as corrupted fs or race with rename) that the call to
lookup_one_unlocked() in reconnect_one() will fail to find the dentry we
are trying to reconnect and instead create a new dentry under the
parent. Now this dentry will not be marked as disconnected although the
parent still may well be disconnected (at least in case this
inconsistency happened because the fs is corrupted and .. doesn't point
to the real parent directory). This creates inconsistency in
disconnected flags but AFAICS it was mostly harmless. At least until
commit f1ee616214 ("VFS: don't keep disconnected dentries on d_anon")
which removed adding of most disconnected dentries to sb->s_anon list.
Thus after this commit cleanup of disconnected dentries implicitely
relies on the fact that dput() will immediately reclaim such dentries.
However when some leaf dentry isn't marked as disconnected, as in the
scenario described above, the reclaim doesn't happen and the dentries
are "leaked". Memory reclaim can eventually reclaim them but otherwise
they stay in memory and if umount comes first, we hit infamous "Busy
inodes after unmount" bug. Make sure all dentries created under a
disconnected parent are marked as disconnected as well.
Reported-by: syzbot+1d79ebe5383fc016cf07@syzkaller.appspotmail.com
Fixes: f1ee616214 ("VFS: don't keep disconnected dentries on d_anon")
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Turn dentry->d_name into an anon union of const struct qsrt (d_name
itself) and a writable alias (__d_name). With constification of some
struct qstr * arguments of functions that get &dentry->d_name passed
to them, that ends up with all modifications provably done only in
fs/dcache.c (and a fairly small part of it).
Any new places doing modifications will be easy to find - grep for
__d_name will suffice.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Merge tag 'pull-qstr' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull d_name audit update from Al Viro:
"Simplifying ->d_name audits, easy part.
Turn dentry->d_name into an anon union of const struct qsrt (d_name
itself) and a writable alias (__d_name).
With constification of some struct qstr * arguments of functions that
get &dentry->d_name passed to them, that ends up with all
modifications provably done only in fs/dcache.c (and a fairly small
part of it).
Any new places doing modifications will be easy to find - grep for
__d_name will suffice"
* tag 'pull-qstr' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
make it easier to catch those who try to modify ->d_name
generic_ci_validate_strict_name(): constify name argument
afs_dir_search: constify qstr argument
afs_edit_dir_{add,remove}(): constify qstr argument
exfat_find(): constify qstr argument
security_dentry_init_security(): constify qstr argument
* saner handling of guards in fs/namespace.c, getting
rid of needlessly strong locking in some of the users.
* lock_mount() calling conventions change - have it set
the environment for attaching to given location, storing the
results in caller-supplied object, without altering the passed
struct path. Make unlock_mount() called as __cleanup for those
objects. It's not exactly guard(), but similar to it.
* MNT_WRITE_HOLD done right - mnt_hold_writers() does *not*
mess with ->mnt_flags anymore, so insertion of a new mount into
->s_mounts of underlying superblock does not, in itself, expose
->mnt_flags of that mount to concurrent modifications.
* getting rid of pathological cases when umount() spends
quadratic time removing the victims from propagation graph -
part of that had been dealt with last cycle, this should finish
it.
* a bunch of stuff constified.
* assorted cleanups.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Merge tag 'pull-mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull vfs mount updates from Al Viro:
"Several piles this cycle, this mount-related one being the largest and
trickiest:
- saner handling of guards in fs/namespace.c, getting rid of
needlessly strong locking in some of the users
- lock_mount() calling conventions change - have it set the
environment for attaching to given location, storing the results in
caller-supplied object, without altering the passed struct path.
Make unlock_mount() called as __cleanup for those objects. It's not
exactly guard(), but similar to it
- MNT_WRITE_HOLD done right.
mnt_hold_writers() does *not* mess with ->mnt_flags anymore, so
insertion of a new mount into ->s_mounts of underlying superblock
does not, in itself, expose ->mnt_flags of that mount to concurrent
modifications
- getting rid of pathological cases when umount() spends quadratic
time removing the victims from propagation graph - part of that had
been dealt with last cycle, this should finish it
- a bunch of stuff constified
- assorted cleanups
* tag 'pull-mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (64 commits)
constify {__,}mnt_is_readonly()
WRITE_HOLD machinery: no need for to bump mount_lock seqcount
struct mount: relocate MNT_WRITE_HOLD bit
preparations to taking MNT_WRITE_HOLD out of ->mnt_flags
setup_mnt(): primitive for connecting a mount to filesystem
simplify the callers of mnt_unhold_writers()
copy_mnt_ns(): use guards
copy_mnt_ns(): use the regular mechanism for freeing empty mnt_ns on failure
open_detached_copy(): separate creation of namespace into helper
open_detached_copy(): don't bother with mount_lock_hash()
path_has_submounts(): use guard(mount_locked_reader)
fs/namespace.c: sanitize descriptions for {__,}lookup_mnt()
ecryptfs: get rid of pointless mount references in ecryptfs dentries
umount_tree(): take all victims out of propagation graph at once
do_mount(): use __free(path_put)
do_move_mount_old(): use __free(path_put)
constify can_move_mount_beneath() arguments
path_umount(): constify struct path argument
may_copy_tree(), __do_loopback(): constify struct path argument
path_mount(): constify struct path argument
...
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Merge tag 'vfs-6.18-rc1.afs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull afs updates from Christian Brauner:
"This contains the change to enable afs to support RENAME_NOREPLACE and
RENAME_EXCHANGE if the server supports it"
* tag 'vfs-6.18-rc1.afs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
afs: Add support for RENAME_NOREPLACE and RENAME_EXCHANGE
Add support for RENAME_NOREPLACE and RENAME_EXCHANGE, if the server
supports them.
The default is translated to YFS.Rename_Replace, falling back to
YFS.Rename; RENAME_NOREPLACE is translated to YFS.Rename_NoReplace and
RENAME_EXCHANGE to YFS.Rename_Exchange, both of which fall back to
reporting EINVAL.
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/740476.1758718189@warthog.procyon.org.uk
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Dan Carpenter <dan.carpenter@linaro.org>
cc: linux-afs@lists.infradead.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Needed there since the callback passed to d_walk() (path_check_mount())
is using __path_is_mountpoint(), which uses __lookup_mnt().
Has to be taken in the caller - d_walk() might take rename_lock spinlock
component and that nests inside mount_lock.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Turn d_name into an anon union of const struct qstr d_name with
struct qstr __d_name. Very few places need to modify it (all
in fs/dcache.c); those are switched to use of ->__d_name.
Note that ->d_name can actually change under you unless you have
the right locking environment; this const just prohibits accidentally
doing stores without being easily spotted.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Use try_cmpxchg() instead of cmpxchg(*ptr, old, new) == old.
The x86 CMPXCHG instruction returns success in the ZF flag,
so this change saves a compare after CMPXCHG (and related
move instruction in front of CMPXCHG).
Note that the value from *ptr should be read using READ_ONCE() to
prevent the compiler from merging, refetching or reordering the read.
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/20250811125308.616717-1-ubizjak@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Merge tag 'vfs-6.17-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull misc VFS updates from Christian Brauner:
"This contains the usual selections of misc updates for this cycle.
Features:
- Add ext4 IOCB_DONTCACHE support
This refactors the address_space_operations write_begin() and
write_end() callbacks to take const struct kiocb * as their first
argument, allowing IOCB flags such as IOCB_DONTCACHE to propagate
to the filesystem's buffered I/O path.
Ext4 is updated to implement handling of the IOCB_DONTCACHE flag
and advertises support via the FOP_DONTCACHE file operation flag.
Additionally, the i915 driver's shmem write paths are updated to
bypass the legacy write_begin/write_end interface in favor of
directly calling write_iter() with a constructed synchronous kiocb.
Another i915 change replaces a manual write loop with
kernel_write() during GEM shmem object creation.
Cleanups:
- don't duplicate vfs_open() in kernel_file_open()
- proc_fd_getattr(): don't bother with S_ISDIR() check
- fs/ecryptfs: replace snprintf with sysfs_emit in show function
- vfs: Remove unnecessary list_for_each_entry_safe() from
evict_inodes()
- filelock: add new locks_wake_up_waiter() helper
- fs: Remove three arguments from block_write_end()
- VFS: change old_dir and new_dir in struct renamedata to dentrys
- netfs: Remove unused declaration netfs_queue_write_request()
Fixes:
- eventpoll: Fix semi-unbounded recursion
- eventpoll: fix sphinx documentation build warning
- fs/read_write: Fix spelling typo
- fs: annotate data race between poll_schedule_timeout() and
pollwake()
- fs/pipe: set FMODE_NOWAIT in create_pipe_files()
- docs/vfs: update references to i_mutex to i_rwsem
- fs/buffer: remove comment about hard sectorsize
- fs/buffer: remove the min and max limit checks in __getblk_slow()
- fs/libfs: don't assume blocksize <= PAGE_SIZE in
generic_check_addressable
- fs_context: fix parameter name in infofc() macro
- fs: Prevent file descriptor table allocations exceeding INT_MAX"
* tag 'vfs-6.17-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (24 commits)
netfs: Remove unused declaration netfs_queue_write_request()
eventpoll: fix sphinx documentation build warning
ext4: support uncached buffered I/O
mm/pagemap: add write_begin_get_folio() helper function
fs: change write_begin/write_end interface to take struct kiocb *
drm/i915: Refactor shmem_pwrite() to use kiocb and write_iter
drm/i915: Use kernel_write() in shmem object create
eventpoll: Fix semi-unbounded recursion
vfs: Remove unnecessary list_for_each_entry_safe() from evict_inodes()
fs/libfs: don't assume blocksize <= PAGE_SIZE in generic_check_addressable
fs/buffer: remove the min and max limit checks in __getblk_slow()
fs: Prevent file descriptor table allocations exceeding INT_MAX
fs: Remove three arguments from block_write_end()
fs/ecryptfs: replace snprintf with sysfs_emit in show function
fs: annotate suspected data race between poll_schedule_timeout() and pollwake()
docs/vfs: update references to i_mutex to i_rwsem
fs/buffer: remove comment about hard sectorsize
fs_context: fix parameter name in infofc() macro
VFS: change old_dir and new_dir in struct renamedata to dentrys
proc_fd_getattr(): don't bother with S_ISDIR() check
...
VFS has switched to i_rwsem for ten years now (9902af79c01a: parallel
lookups actual switch to rwsem), but the VFS documentation and comments
still has references to i_mutex.
Signed-off-by: Junxuan Liao <ljx@cs.wisc.edu>
Link: https://lore.kernel.org/72223729-5471-474a-af3c-f366691fba82@cs.wisc.edu
Signed-off-by: Christian Brauner <brauner@kernel.org>
Do that before new dentry is visible anywhere. It does create
a new possible state for dentries present in ->d_children/->d_sib -
DCACHE_PAR_LOOKUP present, negative, unhashed, not in in-lookup
hash chains, refcount positive. Those are going to be skipped
by all tree-walkers (both d_walk() callbacks in fs/dcache.c and
explicit loops over children/sibling lists elsewhere) and
dput() is fine with those.
NOTE: dropping the final reference to a "normal" in-lookup dentry
(in in-lookup hash) is a bug - somebody must've forgotten to
call d_lookup_done() on it and bad things will happen. With those
it's OK; if/when we get around to making __dentry_kill() complain
about such breakage, remember that predicate to check should
*not* be just d_in_lookup(victim) but rather a combination of that
with !hlist_bl_unhashed(&victim->d_u.d_in_lookup_hash). Might
be worth considering later...
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Convert the last user (d_alloc_pseudo()) and be done with that.
Any out-of-tree filesystem using it should switch to d_splice_alias_ops()
or, better yet, check whether it really needs to have ->d_op vary among
its dentries.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
... and store it in ->s_d_flags, to be used by __d_alloc()
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
DCACHE_OP_PRUNE in ->d_flags at the time of d_set_d_op() should've
been treated the same as any other DCACHE_OP_... - we forgot to adjust
that WARN_ON() when DCACHE_OP_PRUNE had been introduced...
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
... to be used instead of manually assigning to ->s_d_op.
All in-tree filesystem converted (and field itself is renamed,
so any out-of-tree ones in need of conversion will be caught
by compiler).
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Uses of d_set_d_op() on live dentry can be very dangerous; it is going
to be withdrawn and replaced with saner things.
The best way for a filesystem is to have the default dentry_operations
set at mount time and be done with that - __d_alloc() will use that.
Currently there are two cases when d_set_d_op() is used on a live dentry -
one is procfs, which has several genuinely different dentry_operations
instances (different ->d_revalidate(), etc.) and another is
simple_lookup(), where we would be better off without overriding ->d_op.
For procfs we have d_set_d_op() calls followed by d_splice_alias();
provide a new helper (d_splice_alias_ops(inode, dentry, d_ops)) that would
combine those two, and do the d_set_d_op() part while under ->d_lock.
That eliminates one of the places where ->d_flags had been modified
without holding ->d_lock; current behaviour is not racy, but the reasons
for that are far too brittle. Better move to uniform locking rules and
simpler proof of correctness...
The next commit will convert procfs to use of that helper; it is not
exported and won't be until somebody comes up with convincing modular
user for it.
Again, the best approach is to have default ->d_op and let __d_alloc()
do the right thing; filesystem _may_ need non-uniform ->d_op (procfs
does), but there'd better be good reasons for that.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
IOW, read_seqlock_excl() is sufficient there; no need to bother
with write_seqlock() (forcing all rename_lock readers into retry).
That leaves rename_lock taken for write only when we want to change
someone's parent or name.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Merge tag 'vfs-6.16-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull misc vfs updates from Christian Brauner:
"This contains the usual selections of misc updates for this cycle.
Features:
- Use folios for symlinks in the page cache
FUSE already uses folios for its symlinks. Mirror that conversion
in the generic code and the NFS code. That lets us get rid of a few
folio->page->folio conversions in this path, and some of the few
remaining users of read_cache_page() / read_mapping_page()
- Try and make a few filesystem operations killable on the VFS
inode->i_mutex level
- Add sysctl vfs_cache_pressure_denom for bulk file operations
Some workloads need to preserve more dentries than we currently
allow through out sysctl interface
A HDFS servers with 12 HDDs per server, on a HDFS datanode startup
involves scanning all files and caching their metadata (including
dentries and inodes) in memory. Each HDD contains approximately 2
million files, resulting in a total of ~20 million cached dentries
after initialization
To minimize dentry reclamation, they set vfs_cache_pressure to 1.
Despite this configuration, memory pressure conditions can still
trigger reclamation of up to 50% of cached dentries, reducing the
cache from 20 million to approximately 10 million entries. During
the subsequent cache rebuild period, any HDFS datanode restart
operation incurs substantial latency penalties until full cache
recovery completes
To maintain service stability, more dentries need to be preserved
during memory reclamation. The current minimum reclaim ratio (1/100
of total dentries) remains too aggressive for such workload. This
patch introduces vfs_cache_pressure_denom for more granular cache
pressure control
The configuration [vfs_cache_pressure=1,
vfs_cache_pressure_denom=10000] effectively maintains the full 20
million dentry cache under memory pressure, preventing datanode
restart performance degradation
- Avoid some jumps in inode_permission() using likely()/unlikely()
- Avid a memory access which is most likely a cache miss when
descending into devcgroup_inode_permission()
- Add fastpath predicts for stat() and fdput()
- Anonymous inodes currently don't come with a proper mode causing
issues in the kernel when we want to add useful VFS debug assert.
Fix that by giving them a proper mode and masking it off when we
report it to userspace which relies on them not having any mode
- Anonymous inodes currently allow to change inode attributes because
the VFS falls back to simple_setattr() if i_op->setattr isn't
implemented. This means the ownership and mode for every single
user of anon_inode_inode can be changed. Block that as it's either
useless or actively harmful. If specific ownership is needed the
respective subsystem should allocate anonymous inodes from their
own private superblock
- Raise SB_I_NODEV and SB_I_NOEXEC on the anonymous inode superblock
- Add proper tests for anonymous inode behavior
- Make it easy to detect proper anonymous inodes and to ensure that
we can detect them in codepaths such as readahead()
Cleanups:
- Port pidfs to the new anon_inode_{g,s}etattr() helpers
- Try to remove the uselib() system call
- Add unlikely branch hint return path for poll
- Add unlikely branch hint on return path for core_sys_select
- Don't allow signals to interrupt getdents copying for fuse
- Provide a size hint to dir_context for during readdir()
- Use writeback_iter directly in mpage_writepages
- Update compression and mtime descriptions in initramfs
documentation
- Update main netfs API document
- Remove useless plus one in super_cache_scan()
- Remove unnecessary NULL-check guards during setns()
- Add separate separate {get,put}_cgroup_ns no-op cases
Fixes:
- Fix typo in root= kernel parameter description
- Use KERN_INFO for infof()|info_plog()|infofc()
- Correct comments of fs_validate_description()
- Mark an unlikely if condition with unlikely() in
vfs_parse_monolithic_sep()
- Delete macro fsparam_u32hex()
- Remove unused and problematic validate_constant_table()
- Fix potential unsigned integer underflow in fs_name()
- Make file-nr output the total allocated file handles"
* tag 'vfs-6.16-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (43 commits)
fs: Pass a folio to page_put_link()
nfs: Use a folio in nfs_get_link()
fs: Convert __page_get_link() to use a folio
fs/read_write: make default_llseek() killable
fs/open: make do_truncate() killable
fs/open: make chmod_common() and chown_common() killable
include/linux/fs.h: add inode_lock_killable()
readdir: supply dir_context.count as readdir buffer size hint
vfs: Add sysctl vfs_cache_pressure_denom for bulk file operations
fuse: don't allow signals to interrupt getdents copying
Documentation: fix typo in root= kernel parameter description
include/cgroup: separate {get,put}_cgroup_ns no-op case
kernel/nsproxy: remove unnecessary guards
fs: use writeback_iter directly in mpage_writepages
fs: remove useless plus one in super_cache_scan()
fs: add S_ANON_INODE
fs: remove uselib() system call
device_cgroup: avoid access to ->i_rdev in the common case in devcgroup_inode_permission()
fs/fs_parse: Remove unused and problematic validate_constant_table()
fs: touch up predicts in inode_permission()
...
On our HDFS servers with 12 HDDs per server, a HDFS datanode[0] startup
involves scanning all files and caching their metadata (including dentries
and inodes) in memory. Each HDD contains approximately 2 million files,
resulting in a total of ~20 million cached dentries after initialization.
To minimize dentry reclamation, we set vfs_cache_pressure to 1. Despite
this configuration, memory pressure conditions can still trigger
reclamation of up to 50% of cached dentries, reducing the cache from 20
million to approximately 10 million entries. During the subsequent cache
rebuild period, any HDFS datanode restart operation incurs substantial
latency penalties until full cache recovery completes.
To maintain service stability, we need to preserve more dentries during
memory reclamation. The current minimum reclaim ratio (1/100 of total
dentries) remains too aggressive for our workload. This patch introduces
vfs_cache_pressure_denom for more granular cache pressure control. The
configuration [vfs_cache_pressure=1, vfs_cache_pressure_denom=10000]
effectively maintains the full 20 million dentry cache under memory
pressure, preventing datanode restart performance degradation.
Link: https://hadoop.apache.org/docs/r1.2.1/hdfs_design.html#NameNode+and+DataNodes [0]
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/20250511083624.9305-1-laoar.shao@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
try_lookup_noperm() and d_hash_and_lookup() are nearly identical. The
former does some validation of the name where the latter doesn't.
Outside of the VFS that validation is likely valuable, and having only
one exported function for this task is certainly a good idea.
So make d_hash_and_lookup() local to VFS files and change all other
callers to try_lookup_noperm(). Note that the arguments are swapped.
Signed-off-by: NeilBrown <neilb@suse.de>
Link: https://lore.kernel.org/r/20250319031545.2999807-6-neil@brown.name
Signed-off-by: Christian Brauner <brauner@kernel.org>
* Move vm_table members out of kernel/sysctl.c
All vm_table array members have moved to their respective subsystems leading
to the removal of vm_table from kernel/sysctl.c. This increases modularity by
placing the ctl_tables closer to where they are actually used and at the same
time reducing the chances of merge conflicts in kernel/sysctl.c.
* ctl_table range fixes
Replace the proc_handler function that checks variable ranges in
coredump_sysctls and vdso_table with the one that actually uses the extra{1,2}
pointers as min/max values. This tightens the range of the values that users
can pass into the kernel effectively preventing {under,over}flows.
* Misc fixes
Correct grammar errors and typos in test messages. Update sysctl files in
MAINTAINERS. Constified and removed array size in declaration for
alignment_tbl
* Testing
- These have all been in linux-next for at least 1 month
- They have gone through 0-day
- Ran all these through sysctl selftests in x86_64
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Merge tag 'sysctl-6.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/sysctl/sysctl
Pull sysctl updates from Joel Granados:
- Move vm_table members out of kernel/sysctl.c
All vm_table array members have moved to their respective subsystems
leading to the removal of vm_table from kernel/sysctl.c. This
increases modularity by placing the ctl_tables closer to where they
are actually used and at the same time reducing the chances of merge
conflicts in kernel/sysctl.c.
- ctl_table range fixes
Replace the proc_handler function that checks variable ranges in
coredump_sysctls and vdso_table with the one that actually uses the
extra{1,2} pointers as min/max values. This tightens the range of the
values that users can pass into the kernel effectively preventing
{under,over}flows.
- Misc fixes
Correct grammar errors and typos in test messages. Update sysctl
files in MAINTAINERS. Constified and removed array size in
declaration for alignment_tbl
* tag 'sysctl-6.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/sysctl/sysctl: (22 commits)
selftests/sysctl: fix wording of help messages
selftests: fix spelling/grammar errors in sysctl/sysctl.sh
MAINTAINERS: Update sysctl file list in MAINTAINERS
sysctl: Fix underflow value setting risk in vm_table
coredump: Fixes core_pipe_limit sysctl proc_handler
sysctl: remove unneeded include
sysctl: remove the vm_table
sh: vdso: move the sysctl to arch/sh/kernel/vsyscall/vsyscall.c
x86: vdso: move the sysctl to arch/x86/entry/vdso/vdso32-setup.c
fs: dcache: move the sysctl to fs/dcache.c
sunrpc: simplify rpcauth_cache_shrink_count()
fs: drop_caches: move sysctl to fs/drop_caches.c
fs: fs-writeback: move sysctl to fs/fs-writeback.c
mm: nommu: move sysctl to mm/nommu.c
security: min_addr: move sysctl to security/min_addr.c
mm: mmap: move sysctl to mm/mmap.c
mm: util: move sysctls to mm/util.c
mm: vmscan: move vmscan sysctls to mm/vmscan.c
mm: swap: move sysctl to mm/swap.c
mm: filemap: move sysctl to mm/filemap.c
...
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Merge tag 'vfs-6.15-rc1.async.dir' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull vfs async dir updates from Christian Brauner:
"This contains cleanups that fell out of the work from async directory
handling:
- Change kern_path_locked() and user_path_locked_at() to never return
a negative dentry. This simplifies the usability of these helpers
in various places
- Drop d_exact_alias() from the remaining place in NFS where it is
still used. This also allows us to drop the d_exact_alias() helper
completely
- Drop an unnecessary call to fh_update() from nfsd_create_locked()
- Change i_op->mkdir() to return a struct dentry
Change vfs_mkdir() to return a dentry provided by the filesystems
which is hashed and positive. This allows us to reduce the number
of cases where the resulting dentry is not positive to very few
cases. The code in these places becomes simpler and easier to
understand.
- Repack DENTRY_* and LOOKUP_* flags"
* tag 'vfs-6.15-rc1.async.dir' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
doc: fix inline emphasis warning
VFS: Change vfs_mkdir() to return the dentry.
nfs: change mkdir inode_operation to return alternate dentry if needed.
fuse: return correct dentry for ->mkdir
ceph: return the correct dentry on mkdir
hostfs: store inode in dentry after mkdir if possible.
Change inode_operations.mkdir to return struct dentry *
nfsd: drop fh_update() from S_IFDIR branch of nfsd_create_locked()
nfs/vfs: discard d_exact_alias()
VFS: add common error checks to lookup_one_qstr_excl()
VFS: change kern_path_locked() and user_path_locked_at() to never return negative dentry
VFS: repack LOOKUP_ bit flags.
VFS: repack DENTRY_ flags.
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Merge tag 'vfs-6.15-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull misc vfs updates from Christian Brauner:
"Features:
- Add CONFIG_DEBUG_VFS infrastucture:
- Catch invalid modes in open
- Use the new debug macros in inode_set_cached_link()
- Use debug-only asserts around fd allocation and install
- Place f_ref to 3rd cache line in struct file to resolve false
sharing
Cleanups:
- Start using anon_inode_getfile_fmode() helper in various places
- Don't take f_lock during SEEK_CUR if exclusion is guaranteed by
f_pos_lock
- Add unlikely() to kcmp()
- Remove legacy ->remount_fs method from ecryptfs after port to the
new mount api
- Remove invalidate_inodes() in favour of evict_inodes()
- Simplify ep_busy_loopER by removing unused argument
- Avoid mmap sem relocks when coredumping with many missing pages
- Inline getname()
- Inline new_inode_pseudo() and de-staticize alloc_inode()
- Dodge an atomic in putname if ref == 1
- Consistently deref the files table with rcu_dereference_raw()
- Dedup handling of struct filename init and refcounts bumps
- Use wq_has_sleeper() in end_dir_add()
- Drop the lock trip around I_NEW wake up in evict()
- Load the ->i_sb pointer once in inode_sb_list_{add,del}
- Predict not reaching the limit in alloc_empty_file()
- Tidy up do_sys_openat2() with likely/unlikely
- Call inode_sb_list_add() outside of inode hash lock
- Sort out fd allocation vs dup2 race commentary
- Turn page_offset() into a wrapper around folio_pos()
- Remove locking in exportfs around ->get_parent() call
- try_lookup_one_len() does not need any locks in autofs
- Fix return type of several functions from long to int in open
- Fix return type of several functions from long to int in ioctls
Fixes:
- Fix watch queue accounting mismatch"
* tag 'vfs-6.15-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (30 commits)
fs: sort out fd allocation vs dup2 race commentary, take 2
fs: call inode_sb_list_add() outside of inode hash lock
fs: tidy up do_sys_openat2() with likely/unlikely
fs: predict not reaching the limit in alloc_empty_file()
fs: load the ->i_sb pointer once in inode_sb_list_{add,del}
fs: drop the lock trip around I_NEW wake up in evict()
fs: use wq_has_sleeper() in end_dir_add()
VFS/autofs: try_lookup_one_len() does not need any locks
fs: dedup handling of struct filename init and refcounts bumps
fs: consistently deref the files table with rcu_dereference_raw()
exportfs: remove locking around ->get_parent() call.
fs: use debug-only asserts around fd allocation and install
fs: dodge an atomic in putname if ref == 1
vfs: Remove invalidate_inodes()
ecryptfs: remove NULL remount_fs from super_operations
watch_queue: fix pipe accounting mismatch
fs: place f_ref to 3rd cache line in struct file to resolve false sharing
epoll: simplify ep_busy_loop by removing always 0 argument
fs: Turn page_offset() into a wrapper around folio_pos()
kcmp: improve performance adding an unlikely hint to task comparisons
...
The routine is used a lot, while the wakeup almost never has anyone to
deal with.
wake_up_all() takes an irq-protected spinlock, wq_has_sleeper() "only"
contains a full fence -- not free by any means, but still cheaper.
Sample result tracing waiters using a custom probe during -j 20 kernel
build (0 - no waiters, 1 - waiters):
@[
wakeprobe+5
__wake_up_common+63
__wake_up+54
__d_add+234
d_splice_alias+146
ext4_lookup+439
path_openat+1746
do_filp_open+195
do_sys_openat2+153
__x64_sys_openat+86
do_syscall_64+82
entry_SYSCALL_64_after_hwframe+118
]:
[0, 1) 13999 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[1, ...) 1 | |
Only 1 call out of 14000 with this backtrace had waiters.
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20250316232421.1642758-1-mjguzik@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
d_exact_alias() is a descendent of d_add_unique() which was introduced
20 years ago mostly likely to work around problems with NFS servers of
the time. It is now not used in several situations were it was
originally needed and there have been no reports of problems -
presumably the old NFS servers have been improved. This only place it
is now use is in NFSv4 code and the old problematic servers are thought
to have been v2/v3 only.
There is no clear benefit in reusing a unhashed() dentry which happens
to have the same name as the dentry we are adding.
So this patch removes d_exact_alias() and the one place that it is used.
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Link: https://lore.kernel.org/r/20250226062135.2043651-2-neilb@suse.de
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Merge tag 'vfs-6.14-rc2.fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull vfs fixes from Christian Brauner:
- Fix fsnotify FMODE_NONOTIFY* handling.
This also disables fsnotify on all pseudo files by default apart from
very select exceptions. This carries a regression risk so we need to
watch out and adapt accordingly. However, it is overall a significant
improvement over the current status quo where every rando file can
get fsnotify enabled.
- Cleanup and simplify lockref_init() after recent lockref changes.
- Fix vboxfs build with gcc-15.
- Add an assert into inode_set_cached_link() to catch corrupt links.
- Allow users to also use an empty string check to detect whether a
given mount option string was empty or not.
- Fix how security options were appended to statmount()'s ->mnt_opt
field.
- Fix statmount() selftests to always check the returned mask.
- Fix uninitialized value in vfs_statx_path().
- Fix pidfs_ioctl() sanity checks to guard against ioctl() overloading
and preserve extensibility.
* tag 'vfs-6.14-rc2.fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
vfs: sanity check the length passed to inode_set_cached_link()
pidfs: improve ioctl handling
fsnotify: disable pre-content and permission events by default
selftests: always check mask returned by statmount(2)
fsnotify: disable notification by default for all pseudo files
fs: fix adding security options to statmount.mnt_opt
fsnotify: use accessor to set FMODE_NONOTIFY_*
lockref: remove count argument of lockref_init
gfs2: switch to lockref_init(..., 1)
gfs2: use lockref_init for gl_lockref
statmount: let unset strings be empty
vboxsf: fix building with GCC 15
fs/stat.c: avoid harmless garbage value problem in vfs_statx_path()
The sysctl_vfs_cache_pressure belongs to fs/dcache.c, move it to
fs/dcache.c from kernel/sysctl.c. As a part of fs/dcache.c cleaning,
sysctl_vfs_cache_pressure is changed to a static variable, and change
the inline-type function vfs_pressure_ratio() to out-of-inline type,
export vfs_pressure_ratio() with EXPORT_SYMBOL_GPL to be used by other
files. Move the unneeded include(linux/dcache.h).
Signed-off-by: Kaixiong Yu <yukaixiong@huawei.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Joel Granados <joel.granados@kernel.org>
All users of lockref_init() now initialize the count to 1, so hardcode
that and remove the count argument.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Link: https://lore.kernel.org/r/20250130135624.1899988-4-agruenba@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Merge tag 'pull-fix' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull d_revalidate fix from Al Viro:
"Fix a braino in d_revalidate series: check ->d_op for NULL"
* tag 'pull-fix' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
fix braino in "9p: fix ->rename_sem exclusion"
->d_op can bloody well be NULL
Fucked-up-by: Al Viro <viro@zeniv.linux.org.uk>
Fixes: 30d61efe11 "9p: fix ->rename_sem exclusion"
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Most of the filesystem methods where we care about dentry name
and parent have their stability guaranteed by the callers;
->d_revalidate() is the major exception.
It's easy enough for callers to supply stable values for
expected name and expected parent of the dentry being
validated. That kills quite a bit of boilerplate in
->d_revalidate() instances, along with a bunch of races
where they used to access ->d_name without sufficient
precautions.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Merge tag 'pull-revalidate' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull vfs d_revalidate updates from Al Viro:
"Provide stable parent and name to ->d_revalidate() instances
Most of the filesystem methods where we care about dentry name and
parent have their stability guaranteed by the callers;
->d_revalidate() is the major exception.
It's easy enough for callers to supply stable values for expected name
and expected parent of the dentry being validated. That kills quite a
bit of boilerplate in ->d_revalidate() instances, along with a bunch
of races where they used to access ->d_name without sufficient
precautions"
* tag 'pull-revalidate' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
9p: fix ->rename_sem exclusion
orangefs_d_revalidate(): use stable parent inode and name passed by caller
ocfs2_dentry_revalidate(): use stable parent inode and name passed by caller
nfs: fix ->d_revalidate() UAF on ->d_name accesses
nfs{,4}_lookup_validate(): use stable parent inode passed by caller
gfs2_drevalidate(): use stable parent inode and name passed by caller
fuse_dentry_revalidate(): use stable parent inode and name passed by caller
vfat_revalidate{,_ci}(): use stable parent inode passed by caller
exfat_d_revalidate(): use stable parent inode passed by caller
fscrypt_d_revalidate(): use stable parent inode passed by caller
ceph_d_revalidate(): propagate stable name down into request encoding
ceph_d_revalidate(): use stable parent inode passed by caller
afs_d_revalidate(): use stable name and parent inode passed by caller
Pass parent directory inode and expected name to ->d_revalidate()
generic_ci_d_compare(): use shortname_storage
ext4 fast_commit: make use of name_snapshot primitives
dissolve external_name.u into separate members
make take_dentry_name_snapshot() lockless
dcache: back inline names with a struct-wrapped array of unsigned long
make sure that DNAME_INLINE_LEN is a multiple of word size
Add the const qualifier to all the ctl_tables in the tree except for
watchdog_hardlockup_sysctl, memory_allocation_profiling_sysctls,
loadpin_sysctl_table and the ones calling register_net_sysctl (./net,
drivers/inifiniband dirs). These are special cases as they use a
registration function with a non-const qualified ctl_table argument or
modify the arrays before passing them on to the registration function.
Constifying ctl_table structs will prevent the modification of
proc_handler function pointers as the arrays would reside in .rodata.
This is made possible after commit 78eb4ea25c ("sysctl: treewide:
constify the ctl_table argument of proc_handlers") constified all the
proc_handlers.
Created this by running an spatch followed by a sed command:
Spatch:
virtual patch
@
depends on !(file in "net")
disable optional_qualifier
@
identifier table_name != {
watchdog_hardlockup_sysctl,
iwcm_ctl_table,
ucma_ctl_table,
memory_allocation_profiling_sysctls,
loadpin_sysctl_table
};
@@
+ const
struct ctl_table table_name [] = { ... };
sed:
sed --in-place \
-e "s/struct ctl_table .table = &uts_kern/const struct ctl_table *table = \&uts_kern/" \
kernel/utsname_sysctl.c
Reviewed-by: Song Liu <song@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org> # for kernel/trace/
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> # SCSI
Reviewed-by: Darrick J. Wong <djwong@kernel.org> # xfs
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Corey Minyard <cminyard@mvista.com>
Acked-by: Wei Liu <wei.liu@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Bill O'Donnell <bodonnel@redhat.com>
Acked-by: Baoquan He <bhe@redhat.com>
Acked-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Acked-by: Anna Schumaker <anna.schumaker@oracle.com>
Signed-off-by: Joel Granados <joel.granados@kernel.org>
9p wants to be able to build a path from given dentry to fs root and keep
it valid over a blocking operation.
->s_vfs_rename_mutex would be a natural candidate, but there are places
where we need that and where we have no way to tell if ->s_vfs_rename_mutex
is already held deeper in callchain. Moreover, it's only held for
cross-directory renames; name changes within the same directory happen
without it.
Solution:
* have d_move() done in ->rename() rather than in its caller
* maintain a 9p-private rwsem (per-filesystem)
* hold it exclusive over the relevant part of ->rename()
* hold it shared over the places where we want the path.
That almost works. FS_RENAME_DOES_D_MOVE is enough to put all d_move()
and d_exchange() calls under filesystem's control. However, there's
also __d_unalias(), which isn't covered by any of that.
If ->lookup() hits a directory inode with preexisting dentry elsewhere
(due to e.g. rename done on server behind our back), d_splice_alias()
called by ->lookup() will move/rename that alias.
Add a couple of optional methods, so that __d_unalias() would do
if alias->d_op->d_unalias_trylock != NULL
if (!alias->d_op->d_unalias_trylock(alias))
fail (resulting in -ESTALE from lookup)
__d_move(...)
if alias->d_op->d_unalias_unlock != NULL
alias->d_unalias_unlock(alias)
where it currently does __d_move(). 9p instances do down_write_trylock()
and up_write() of ->rename_mutex.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
... and document the constraints on the layout. Kept separate from
the previous commit to keep the noise separate from actual changes.
The reason for explicit __aligned() on ->name[] rather than relying
upon the alignment of the previous field is that the previous iteration
of that commit tried to save 4 bytes on 64bit by eliminating a hole
in there, which broke the assumptions in dentry_string_cmp().
Better spell it out and avoid the temptation for the future...
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Use ->d_seq instead of grabbing ->d_lock; in case of shortname dentries
that avoids any stores to shared data objects and in case of long names
we are down to (unavoidable) atomic_inc on the external_name refcount.
Makes the thing safer as well - the areas where ->d_seq is held odd are
all nested inside the areas where ->d_lock is held, and the latter are
much more numerous.
NOTE: now that there is a lockless path where we might try to grab
a reference to an already doomed external_name instance, it is no
longer possible for external_name.u.count and external_name.u.head
to share space (kudos to Linus for spotting that).
To reduce the noise this commit just make external_name.u a struct
(instead of union); the next commit will dissolve it.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
... so that they can be copied with struct assignment (which generates
better code) and accessed word-by-word.
The type is union shortname_storage; it's a union of arrays of
unsigned char and unsigned long.
struct name_snapshot.inline_name turned into union shortname_storage;
users (all in fs/dcache.c) adjusted.
struct dentry.d_iname has some users outside of fs/dcache.c; to
reduce the amount of noise in commit, it is replaced with
union shortname_storage d_shortname and d_iname is turned into a macro
that expands to d_shortname.string (similar to d_lock handling).
That compat macro is temporary - most of the remaining instances will
be taken out by debugfs series, and once that is merged and few others
are taken care of this will go away.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
... calling the number of words DNAME_INLINE_WORDS.
The next step will be to have a structure to hold inline name arrays
(both in dentry and in name_snapshot) and use that to alias the
existing arrays of unsigned char there. That will allow both
full-structure copies and convenient word-by-word accesses.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Linus Torvalds
Mateusz Guzik
Al Viro
Jan Kara
David Howells
Uros Bizjak
Junxuan Liao
Yafang Shao
NeilBrown
Kaixiong Yu
Andreas Gruenbacher
Joel Granados
Christoph Hellwig