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Port the __I_LRU_ISOLATING mechanism to use the new var event mechanism.
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Josef Bacik <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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Port the __I_NEW mechanism to use the new var event mechanism.
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Josef Bacik <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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Port the __I_SYNC mechanism to use the new var event mechanism.
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Josef Bacik <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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so that we can use the first bits to derive unique addresses from
i_state.
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Josef Bacik <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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The i_state member is an unsigned long so that it can be used with the
wait bit infrastructure which expects unsigned long. This wastes 4 bytes
which we're unlikely to ever use. Switch to using the var event wait
mechanism using the address of the bit. Thanks to Linus for the address
idea.
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Josef Bacik <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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Hi, all
Recently I noticed a bug[1] in btrfs, after digged it into
and I believe it'a race in vfs.
Let's assume there's a inode (ie ino 261) with i_count 1 is
called by iput(), and there's a concurrent thread calling
generic_shutdown_super().
cpu0: cpu1:
iput() // i_count is 1
->spin_lock(inode)
->dec i_count to 0
->iput_final() generic_shutdown_super()
->__inode_add_lru() ->evict_inodes()
// cause some reason[2] ->if (atomic_read(inode->i_count)) continue;
// return before // inode 261 passed the above check
// list_lru_add_obj() // and then schedule out
->spin_unlock()
// note here: the inode 261
// was still at sb list and hash list,
// and I_FREEING|I_WILL_FREE was not been set
btrfs_iget()
// after some function calls
->find_inode()
// found the above inode 261
->spin_lock(inode)
// check I_FREEING|I_WILL_FREE
// and passed
->__iget()
->spin_unlock(inode) // schedule back
->spin_lock(inode)
// check (I_NEW|I_FREEING|I_WILL_FREE) flags,
// passed and set I_FREEING
iput() ->spin_unlock(inode)
->spin_lock(inode) ->evict()
// dec i_count to 0
->iput_final()
->spin_unlock()
->evict()
Now, we have two threads simultaneously evicting
the same inode, which may trigger the BUG(inode->i_state & I_CLEAR)
statement both within clear_inode() and iput().
To fix the bug, recheck the inode->i_count after holding i_lock.
Because in the most scenarios, the first check is valid, and
the overhead of spin_lock() can be reduced.
If there is any misunderstanding, please let me know, thanks.
[1]: https://lore.kernel.org/linux-btrfs/[email protected]/
[2]: The reason might be 1. SB_ACTIVE was removed or 2. mapping_shrinkable()
return false when I reproduced the bug.
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=67ba3c42bcbb4665d3ad
CC: [email protected]
Fixes: 63997e98a3be ("split invalidate_inodes()")
Signed-off-by: Julian Sun <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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The VFS git tree is missing from MAINTAINERS. Add it.
Signed-off-by: Eric Biggers <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
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The underscore variants are for uapi whereas the non-underscore variants
are for in-kernel consumers.
Link: https://lore.kernel.org/r/20240822-anwerben-nutzung-1cd6c82a565f@brauner
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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This helper has been unused for a while now.
Link: https://lore.kernel.org/r/20240822-bewuchs-werktag-46672b3c0606@brauner
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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Most commonly neither I_LRU_ISOLATING nor I_SYNC are set, but the stock
kernel takes a back-to-back relock trip to check for them.
It probably can be avoided altogether, but for now massage things back
to just one lock acquire.
Signed-off-by: Mateusz Guzik <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Zhihao Cheng <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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After its conversion to the new mount API, debugfs displays "none" in
/proc/mounts instead of the actual source. Fix this by recognising its
"source" mount option.
Signed-off-by: Marc Aurèle La France <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Fixes: a20971c18752 ("vfs: Convert debugfs to use the new mount API")
Cc: [email protected] # 6.10.x: 49abee5991e1: debugfs: Convert to new uid/gid option parsing helpers
Signed-off-by: Christian Brauner <[email protected]>
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Afaict, we can just rely on inode->i_dio_count for waiting instead of
this awkward indirection through __I_DIO_WAKEUP. This survives LTP dio
and xfstests dio tests.
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Josef Bacik <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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In step 2, we obtain the kernel id `k1000`. So in next step (step
3), we should translate the `k1000` not `k21000`.
Signed-off-by: Hongbo Li <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
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Since in_group_or_capable has been exported, we can use
it to simplify the code when check group and capable.
Signed-off-by: Hongbo Li <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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According to bpftrace on these routines most calls result in cmpxchg,
which already provides the same guarantee.
In inode_maybe_inc_iversion elision is possible because even if the
wrong value was read due to now missing smp_mb fence, the issue is going
to correct itself after cmpxchg. If it appears cmpxchg wont be issued,
the fence + reload are there bringing back previous behavior.
Signed-off-by: Mateusz Guzik <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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Add ability to set per-dentry mount expire timeout to autofs.
There are two fairly well known automounter map formats, the autofs
format and the amd format (more or less System V and Berkley).
Some time ago Linux autofs added an amd map format parser that
implemented a fair amount of the amd functionality. This was done
within the autofs infrastructure and some functionality wasn't
implemented because it either didn't make sense or required extra
kernel changes. The idea was to restrict changes to be within the
existing autofs functionality as much as possible and leave changes
with a wider scope to be considered later.
One of these changes is implementing the amd options:
1) "unmount", expire this mount according to a timeout (same as the
current autofs default).
2) "nounmount", don't expire this mount (same as setting the autofs
timeout to 0 except only for this specific mount) .
3) "utimeout=<seconds>", expire this mount using the specified
timeout (again same as setting the autofs timeout but only for
this mount).
To implement these options per-dentry expire timeouts need to be
implemented for autofs indirect mounts. This is because all map keys
(mounts) for autofs indirect mounts use an expire timeout stored in
the autofs mount super block info. structure and all indirect mounts
use the same expire timeout.
Now I have a request to add the "nounmount" option so I need to add
the per-dentry expire handling to the kernel implementation to do this.
The implementation uses the trailing path component to identify the
mount (and is also used as the autofs map key) which is passed in the
autofs_dev_ioctl structure path field. The expire timeout is passed
in autofs_dev_ioctl timeout field (well, of the timeout union).
If the passed in timeout is equal to -1 the per-dentry timeout and
flag are cleared providing for the "unmount" option. If the timeout
is greater than or equal to 0 the timeout is set to the value and the
flag is also set. If the dentry timeout is 0 the dentry will not expire
by timeout which enables the implementation of the "nounmount" option
for the specific mount. When the dentry timeout is greater than zero it
allows for the implementation of the "utimeout=<seconds>" option.
Signed-off-by: Ian Kent <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
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A soft lockup in ilookup was reported when stress-testing a 512-way
system [1] (see [2] for full context) and it was verified that not
taking the lock shifts issues back to mm.
[1] https://lore.kernel.org/linux-mm/[email protected]/
[2] https://lore.kernel.org/linux-mm/[email protected]/
Signed-off-by: Mateusz Guzik <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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This is another flag that is statically set and doesn't need to use up
an FMODE_* bit. Move it to ->fop_flags and free up another FMODE_* bit.
(1) mem_open() used from proc_mem_operations
(2) adi_open() used from adi_fops
(3) drm_open_helper():
(3.1) accel_open() used from DRM_ACCEL_FOPS
(3.2) drm_open() used from
(3.2.1) amdgpu_driver_kms_fops
(3.2.2) psb_gem_fops
(3.2.3) i915_driver_fops
(3.2.4) nouveau_driver_fops
(3.2.5) panthor_drm_driver_fops
(3.2.6) radeon_driver_kms_fops
(3.2.7) tegra_drm_fops
(3.2.8) vmwgfx_driver_fops
(3.2.9) xe_driver_fops
(3.2.10) DRM_GEM_FOPS
(3.2.11) DEFINE_DRM_GEM_DMA_FOPS
(4) struct memdev sets fmode flags based on type of device opened. For
devices using struct mem_fops unsigned offset is used.
Mark all these file operations as FOP_UNSIGNED_OFFSET and add asserts
into the open helper to ensure that the flag is always set.
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jeff Layton <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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In do_dentry_open() the usage is:
f->f_op = fops_get(inode->i_fop);
In generated asm the compiler emits 2 reads from inode->i_fop instead of
just one.
This popped up due to false-sharing where loads from that offset end up
bouncing a cacheline during parallel open. While this is going to be fixed,
the spurious load does not need to be there.
This makes do_dentry_open() go down from 1177 to 1154 bytes.
fops_put() is patched to maintain some consistency.
No functional changes.
Reviewed-by: Josef Bacik <[email protected]>
Signed-off-by: Mateusz Guzik <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
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Add the __counted_by compiler attribute to the flexible array member
entries to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.
Signed-off-by: Thorsten Blum <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Gustavo A. R. Silva <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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If we find a positive dentry we can now simply try and open it. All
prelimiary checks are already done with or without O_CREAT.
Signed-off-by: Christian Brauner <[email protected]>
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Now that we audit later during lookup_open() we can remove the audit
dummy context check. This simplifies things a lot.
Signed-off-by: Christian Brauner <[email protected]>
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Perform the check for trailing slashes right in the fastpath check and
don't bother with any additional work.
Signed-off-by: Christian Brauner <[email protected]>
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During O_CREAT we unconditionally audit the parent inode. This makes it
difficult to support a fastpath for O_CREAT when the file already exists
because we have to drop out of RCU lookup needlessly.
We worked around this by checking whether audit was actually active but
that's also suboptimal. Instead, move the audit of the parent inode down
into lookup_open() at a point where it's mostly certain that the file
needs to be created.
This also reduced the inconsistency that currently exists: while audit
on the parent is done independent of whether or no the file already
existed an audit on the file is only performed if it has been created.
By moving the audit down a bit we emit the audit a little later but it
will allow us to simplify the fastpath for O_CREAT significantly.
Signed-off-by: Christian Brauner <[email protected]>
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Today, when opening a file we'll typically do a fast lookup, but if
O_CREAT is set, the kernel always takes the exclusive inode lock. I
assume this was done with the expectation that O_CREAT means that we
always expect to do the create, but that's often not the case. Many
programs set O_CREAT even in scenarios where the file already exists.
This patch rearranges the pathwalk-for-open code to also attempt a
fast_lookup in certain O_CREAT cases. If a positive dentry is found, the
inode_lock can be avoided altogether, and if auditing isn't enabled, it
can stay in rcuwalk mode for the last step_into.
One notable exception that is hopefully temporary: if we're doing an
rcuwalk and auditing is enabled, skip the lookup_fast. Legitimizing the
dentry in that case is more expensive than taking the i_rwsem for now.
Signed-off-by: Jeff Layton <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Reviewed-by: Josef Bacik <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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A struct eventpoll's busy_poll_usecs field can be modified via a user
ioctl at any time. All reads of this field should be annotated with
READ_ONCE.
Fixes: 85455c795c07 ("eventpoll: support busy poll per epoll instance")
Cc: [email protected]
Signed-off-by: Martin Karsten <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Joe Damato <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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Remove redundant and unnecessary code.
ep_alloc uses kzalloc to create struct eventpoll, so there is no need to
set fields to defaults of 0. This was accidentally introduced in commit
85455c795c07 ("eventpoll: support busy poll per epoll instance") and
expanded on in follow-up commits.
Signed-off-by: Joe Damato <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Martin Karsten <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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Fixed 3 typos in design.rst
Signed-off-by: Xiaxi Shen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Carlos Maiolino <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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These inlines show up in the fast path (e.g., in do_dentry_open()) and
induce said full barrier regarding i_flctx access when in most cases the
pointer is NULL.
The pointer can be safely checked before issuing the barrier, dodging it
in most cases as a result.
It is plausible the consume fence would be sufficient, but I don't want
to go audit all callers regarding what they before calling here.
Signed-off-by: Mateusz Guzik <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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Cc: Alexander Viro <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: [email protected]
The comment on EXPORT_SYMBOL(close_fd) was added in commit 2ca2a09d6215
("fs: add ksys_close() wrapper; remove in-kernel calls to sys_close()"),
before commit 8760c909f54a ("file: Rename __close_fd to close_fd and remove
the files parameter") gave the function its current name, however commit
1572bfdf21d4 ("file: Replace ksys_close with close_fd") removes the
referenced caller entirely, obsoleting this comment.
Signed-off-by: Joel Savitz <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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replace 'permanetly' with 'permanently' in the comment &
replace 'propogated' with 'propagated' in the comment
Signed-off-by: Yuesong Li <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
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Both i_mode and noexec checks wrapped in WARN_ON stem from an artifact
of the previous implementation. They used to legitimately check for the
condition, but that got moved up in two commits:
633fb6ac3980 ("exec: move S_ISREG() check earlier")
0fd338b2d2cd ("exec: move path_noexec() check earlier")
Instead of being removed said checks are WARN_ON'ed instead, which
has some debug value.
However, the spurious path_noexec check is racy, resulting in
unwarranted warnings should someone race with setting the noexec flag.
One can note there is more to perm-checking whether execve is allowed
and none of the conditions are guaranteed to still hold after they were
tested for.
Additionally this does not validate whether the code path did any perm
checking to begin with -- it will pass if the inode happens to be
regular.
Keep the redundant path_noexec() check even though it's mindless
nonsense checking for guarantee that isn't given so drop the WARN.
Reword the commentary and do small tidy ups while here.
Signed-off-by: Mateusz Guzik <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[brauner: keep redundant path_noexec() check]
Signed-off-by: Christian Brauner <[email protected]>
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The lookup_fast helper in fs/namei.c has some subtlety in how dentries
are returned. Document them.
Signed-off-by: Jeff Layton <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
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This function no longer exists.
Signed-off-by: Jeff Layton <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
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Commit 2eea9ce4310d ("mounts: keep list of mounts in an rbtree")
removed the implementation but leave declaration.
Signed-off-by: Yue Haibing <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
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In the function percpu_rwsem_release, the parameter `read`
is unused, so remove it.
Signed-off-by: Wang Long <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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While the old code did support FSCONFIG_SET_FD, there's no need to
re-get the file the fs_context infrastructure already grabbed for us.
Signed-off-by: Aleksa Sarai <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
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If you pass an fd using FSCONFIG_SET_FD, autofs_parse_fd() "steals" the
param->file and so the fs_context infrastructure will not do fput() for
us.
Fixes: e6ec453bd0f0 ("autofs: convert autofs to use the new mount api")
Signed-off-by: Aleksa Sarai <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
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__percpu annotation of *cpu pointer in struct kioctx is put at
the wrong place, resulting in several sparse warnings:
aio.c:623:24: warning: incorrect type in argument 1 (different address spaces)
aio.c:623:24: expected void [noderef] __percpu *__pdata
aio.c:623:24: got struct kioctx_cpu *cpu
aio.c:788:18: warning: incorrect type in assignment (different address spaces)
aio.c:788:18: expected struct kioctx_cpu *cpu
aio.c:788:18: got struct kioctx_cpu [noderef] __percpu *
aio.c:835:24: warning: incorrect type in argument 1 (different address spaces)
aio.c:835:24: expected void [noderef] __percpu *__pdata
aio.c:835:24: got struct kioctx_cpu *cpu
aio.c:940:16: warning: incorrect type in initializer (different address spaces)
aio.c:940:16: expected void const [noderef] __percpu *__vpp_verify
aio.c:940:16: got struct kioctx_cpu *
aio.c:958:16: warning: incorrect type in initializer (different address spaces)
aio.c:958:16: expected void const [noderef] __percpu *__vpp_verify
aio.c:958:16: got struct kioctx_cpu *
Put __percpu annotation at the right place to fix these warnings.
Signed-off-by: Uros Bizjak <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Cc: Benjamin LaHaise <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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If no page could be allocated, an error pointer was used as format
string in pr_warn.
Rearrange the code to return early in case of OOM. Also add a check
for the return value of d_path.
Fixes: f8b92ba67c5d ("mount: Add mount warning for impending timestamp expiry")
Signed-off-by: Olaf Hering <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[brauner: rewrite commit and commit message]
Signed-off-by: Christian Brauner <[email protected]>
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improved
Fixed-
WARNING: Missing a blank line after declarations
WARNING: Missing a blank line after declarations
Declaration format: improved struct file declaration format
Signed-off-by: Mohit0404 <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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After commit c22198e78d52 ("direct-io: remove random prefetches"), Nothing
in this file needs anything from `linux/prefetch.h`.
Signed-off-by: Youling Tang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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When deactivating any type of superblock, it had to wait for the in-flight
wb switches to be completed. wb switches are executed in inode_switch_wbs_work_fn()
which needs to acquire the wb_switch_rwsem and races against sync_inodes_sb().
If there are too much dirty data in the superblock, the waiting time may increase
significantly.
For superblocks without cgroup writeback such as tmpfs, they have nothing to
do with the wb swithes, so the flushing can be avoided.
Signed-off-by: Haifeng Xu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Suggested-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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Christian Brauner <[email protected]> says:
Systemd has a helper called openat_report_new() that returns whether a
file was created anew or it already existed before for cases where
O_CREAT has to be used without O_EXCL (cf. [1]). That apparently isn't
something that's specific to systemd but it's where I noticed it.
The current logic is that it first attempts to open the file without
O_CREAT | O_EXCL and if it gets ENOENT the helper tries again with both
flags. If that succeeds all is well. If it now reports EEXIST it
retries.
That works fairly well but some corner cases make this more involved. If
this operates on a dangling symlink the first openat() without O_CREAT |
O_EXCL will return ENOENT but the second openat() with O_CREAT | O_EXCL
will fail with EEXIST. The reason is that openat() without O_CREAT |
O_EXCL follows the symlink while O_CREAT | O_EXCL doesn't for security
reasons. So it's not something we can really change unless we add an
explicit opt-in via O_FOLLOW which seems really ugly.
The caller could try and use fanotify() to register to listen for
creation events in the directory before calling openat(). The caller
could then compare the returned tid to its own tid to ensure that even
in threaded environments it actually created the file. That might work
but is a lot of work for something that should be fairly simple and I'm
uncertain about it's reliability.
The caller could use a bpf lsm hook to hook into security_file_open() to
figure out whether they created the file. That also seems a bit wild.
So let's add F_CREATED_QUERY which allows the caller to check whether
they actually did create the file. That has caveats of course but I
don't
think they are problematic:
* In multi-threaded environments a thread can only be sure that it did
create the file if it calls openat() with O_CREAT. In other words,
it's obviously not enough to just go through it's fdtable and check
these fds because another thread could've created the file.
* If there's any codepaths where an openat() with O_CREAT would yield
the same struct file as that of another thread it would obviously
cause wrong results. I'm not aware of any such codepaths from openat()
itself. Imho, that would be a bug.
* Related to the previous point, calling the new fcntl() on files created
and opened via special-purpose system calls or ioctl()s would cause
wrong results only if the affected subsystem a) raises FMODE_CREATED
and b) may return the same struct file for two different calls. I'm
not seeing anything outside of regular VFS code that raises
FMODE_CREATED.
There is code for b) in e.g., the drm layer where the same struct file
is resurfaced but again FMODE_CREATED isn't used and it would be very
misleading if it did.
[1]: https://github.com/systemd/systemd/blob/11d5e2b5fbf9f6bfa5763fd45b56829ad4f0777f/src/basic/fs-util.c#L1078
* patches from https://lore.kernel.org/r/[email protected]:
selftests: add F_CREATED_QUERY tests
fcntl: add F_CREATED_QUERY
Signed-off-by: Christian Brauner <[email protected]>
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Add simple selftests for fcntl(fd, F_CREATED_QUERY, 0).
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>
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Systemd has a helper called openat_report_new() that returns whether a
file was created anew or it already existed before for cases where
O_CREAT has to be used without O_EXCL (cf. [1]). That apparently isn't
something that's specific to systemd but it's where I noticed it.
The current logic is that it first attempts to open the file without
O_CREAT | O_EXCL and if it gets ENOENT the helper tries again with both
flags. If that succeeds all is well. If it now reports EEXIST it
retries.
That works fairly well but some corner cases make this more involved. If
this operates on a dangling symlink the first openat() without O_CREAT |
O_EXCL will return ENOENT but the second openat() with O_CREAT | O_EXCL
will fail with EEXIST. The reason is that openat() without O_CREAT |
O_EXCL follows the symlink while O_CREAT | O_EXCL doesn't for security
reasons. So it's not something we can really change unless we add an
explicit opt-in via O_FOLLOW which seems really ugly.
The caller could try and use fanotify() to register to listen for
creation events in the directory before calling openat(). The caller
could then compare the returned tid to its own tid to ensure that even
in threaded environments it actually created the file. That might work
but is a lot of work for something that should be fairly simple and I'm
uncertain about it's reliability.
The caller could use a bpf lsm hook to hook into security_file_open() to
figure out whether they created the file. That also seems a bit wild.
So let's add F_CREATED_QUERY which allows the caller to check whether
they actually did create the file. That has caveats of course but I
don't think they are problematic:
* In multi-threaded environments a thread can only be sure that it did
create the file if it calls openat() with O_CREAT. In other words,
it's obviously not enough to just go through it's fdtable and check
these fds because another thread could've created the file.
* If there's any codepaths where an openat() with O_CREAT would yield
the same struct file as that of another thread it would obviously
cause wrong results. I'm not aware of any such codepaths from openat()
itself. Imho, that would be a bug.
* Related to the previous point, calling the new fcntl() on files created
and opened via special-purpose system calls or ioctl()s would cause
wrong results only if the affected subsystem a) raises FMODE_CREATED
and b) may return the same struct file for two different calls. I'm
not seeing anything outside of regular VFS code that raises
FMODE_CREATED.
There is code for b) in e.g., the drm layer where the same struct file
is resurfaced but again FMODE_CREATED isn't used and it would be very
misleading if it did.
Link: https://github.com/systemd/systemd/blob/11d5e2b5fbf9f6bfa5763fd45b56829ad4f0777f/src/basic/fs-util.c#L1078 [1]
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jeff Layton <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
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git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core
Pull driver core fixes from Greg KH:
"Here are two driver fixes for regressions from 6.11-rc1 due to the
driver core change making a structure in a driver core callback const.
These were missed by all testing EXCEPT for what Bart happened to be
running, so I appreciate the fixes provided here for some
odd/not-often-used driver subsystems that nothing else happened to
catch.
Both of these fixes have been in linux-next all week with no reported
issues"
* tag 'driver-core-6.11-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core:
mips: sgi-ip22: Fix the build
ARM: riscpc: ecard: Fix the build
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git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc
Pull char / misc fixes from Greg KH:
"Here are some small char/misc fixes for 6.11-rc4 to resolve reported
problems. Included in here are:
- fastrpc revert of a change that broke userspace
- xillybus fixes for reported issues
Half of these have been in linux-next this week with no reported
problems, I don't know if the last bit of xillybus driver changes made
it in, but they are 'obviously correct' so will be safe :)"
* tag 'char-misc-6.11-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc:
char: xillybus: Check USB endpoints when probing device
char: xillybus: Refine workqueue handling
Revert "misc: fastrpc: Restrict untrusted app to attach to privileged PD"
char: xillybus: Don't destroy workqueue from work item running on it
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git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty
Pull tty / serial fixes from Greg KH:
"Here are some small tty and serial driver fixes for 6.11-rc4 to
resolve some reported problems. Included in here are:
- conmakehash.c userspace build issues
- fsl_lpuart driver fix
- 8250_omap revert for reported regression
- atmel_serial rts flag fix
All of these have been in linux-next this week with no reported
issues"
* tag 'tty-6.11-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty:
Revert "serial: 8250_omap: Set the console genpd always on if no console suspend"
tty: atmel_serial: use the correct RTS flag.
tty: vt: conmakehash: remove non-portable code printing comment header
tty: serial: fsl_lpuart: mark last busy before uart_add_one_port
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