file: remove outdated comment after close_fd()

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: linux-fsdevel@vger.kernel.org

file: remove outdated comment after close_fd()

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: linux-fsdevel@vger.kernel.org

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 <jsavitz@redhat.com>
Link: https://lore.kernel.org/r/20240803025455.239276-1-jsavitz@redhat.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

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add struct fd constructors, get rid of __to_fd()

Make __fdget() et.al. return struct fd directly.
New helpers: BORROWED_FD(file) and CLONED_FD(file), for
borrowed and cloned file references resp.

add struct fd constructors, get rid of __to_fd()

Make __fdget() et.al. return struct fd directly.
New helpers: BORROWED_FD(file) and CLONED_FD(file), for
borrowed and cloned file references resp.

NOTE: this might need tuning; in particular, inline on
__fget_light() is there to keep the code generation same as
before - we probably want to keep it inlined in fdget() et.al.
(especially so in fdget_pos()), but that needs profiling.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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fix bitmap corruption on close_range() with CLOSE_RANGE_UNSHARE

copy_fd_bitmaps(new, old, count) is expected to copy the first
count/BITS_PER_LONG bits from old->full_fds_bits[] and fill
the rest wi

fix bitmap corruption on close_range() with CLOSE_RANGE_UNSHARE

copy_fd_bitmaps(new, old, count) is expected to copy the first
count/BITS_PER_LONG bits from old->full_fds_bits[] and fill
the rest with zeroes. What it does is copying enough words
(BITS_TO_LONGS(count/BITS_PER_LONG)), then memsets the rest.
That works fine, *if* all bits past the cutoff point are
clear. Otherwise we are risking garbage from the last word
we'd copied.

For most of the callers that is true - expand_fdtable() has
count equal to old->max_fds, so there's no open descriptors
past count, let alone fully occupied words in ->open_fds[],
which is what bits in ->full_fds_bits[] correspond to.

The other caller (dup_fd()) passes sane_fdtable_size(old_fdt, max_fds),
which is the smallest multiple of BITS_PER_LONG that covers all
opened descriptors below max_fds. In the common case (copying on
fork()) max_fds is ~0U, so all opened descriptors will be below
it and we are fine, by the same reasons why the call in expand_fdtable()
is safe.

Unfortunately, there is a case where max_fds is less than that
and where we might, indeed, end up with junk in ->full_fds_bits[] -
close_range(from, to, CLOSE_RANGE_UNSHARE) with
* descriptor table being currently shared
* 'to' being above the current capacity of descriptor table
* 'from' being just under some chunk of opened descriptors.
In that case we end up with observably wrong behaviour - e.g. spawn
a child with CLONE_FILES, get all descriptors in range 0..127 open,
then close_range(64, ~0U, CLOSE_RANGE_UNSHARE) and watch dup(0) ending
up with descriptor #128, despite #64 being observably not open.

The minimally invasive fix would be to deal with that in dup_fd().
If this proves to add measurable overhead, we can go that way, but
let's try to fix copy_fd_bitmaps() first.

* new helper: bitmap_copy_and_expand(to, from, bits_to_copy, size).
* make copy_fd_bitmaps() take the bitmap size in words, rather than
bits; it's 'count' argument is always a multiple of BITS_PER_LONG,
so we are not losing any information, and that way we can use the
same helper for all three bitmaps - compiler will see that count
is a multiple of BITS_PER_LONG for the large ones, so it'll generate
plain memcpy()+memset().

Reproducer added to tools/testing/selftests/core/close_range_test.c

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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protect the fetch of ->fd[fd] in do_dup2() from mispredictions

both callers have verified that fd is not greater than ->max_fds;
however, misprediction might end up with
tofree = fdt->fd[fd]

protect the fetch of ->fd[fd] in do_dup2() from mispredictions

both callers have verified that fd is not greater than ->max_fds;
however, misprediction might end up with
tofree = fdt->fd[fd];
being speculatively executed. That's wrong for the same reasons
why it's wrong in close_fd()/file_close_fd_locked(); the same
solution applies - array_index_nospec(fd, fdt->max_fds) could differ
from fd only in case of speculative execution on mispredicted path.

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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fs/file: fix the check in find_next_fd()

The maximum possible return value of find_next_zero_bit(fdt->full_fds_bits,
maxbit, bitbit) is maxbit. This return value, multiplied by BITS_PER_LONG,
gives

fs/file: fix the check in find_next_fd()

The maximum possible return value of find_next_zero_bit(fdt->full_fds_bits,
maxbit, bitbit) is maxbit. This return value, multiplied by BITS_PER_LONG,
gives the value of bitbit, which can never be greater than maxfd, it can
only be equal to maxfd at most, so the following check 'if (bitbit > maxfd)'
will never be true.

Moreover, when bitbit equals maxfd, it indicates that there are no unused
fds, and the function can directly return.

Fix this check.

Signed-off-by: Yuntao Wang <yuntao.wang@linux.dev>
Link: https://lore.kernel.org/r/20240529160656.209352-1-yuntao.wang@linux.dev
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

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get_file_rcu(): no need to check for NULL separately

IS_ERR(NULL) is false and IS_ERR() already comes with unlikely()...

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <

get_file_rcu(): no need to check for NULL separately

IS_ERR(NULL) is false and IS_ERR() already comes with unlikely()...

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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fd_is_open(): move to fs/file.c

no users outside that...

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

close_on_exec(): pass files_struct instead of fdtable

both callers are happier that way...

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

file: remove __receive_fd()

Honestly, there's little value in having a helper with and without that
int __user *ufd argument. It's just messy and doesn't really give us
anything. Just expose receive

file: remove __receive_fd()

Honestly, there's little value in having a helper with and without that
int __user *ufd argument. It's just messy and doesn't really give us
anything. Just expose receive_fd() with that argument and get rid of
that helper.

Link: https://lore.kernel.org/r/20231130-vfs-files-fixes-v1-5-e73ca6f4ea83@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>

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file: remove pointless wrapper

Only io_uring uses __close_fd_get_file(). All it does is hide
current->files but io_uring accesses files_struct directly right now
anyway so it's a bit pointless. Just

file: remove pointless wrapper

Only io_uring uses __close_fd_get_file(). All it does is hide
current->files but io_uring accesses files_struct directly right now
anyway so it's a bit pointless. Just rename pick_file() to
file_close_fd_locked() and let io_uring use it. Add a lockdep assert in
there that we expect the caller to hold file_lock while we're at it.

Link: https://lore.kernel.org/r/20231130-vfs-files-fixes-v1-2-e73ca6f4ea83@kernel.org
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

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file: s/close_fd_get_file()/file_close_fd()/g

That really shouldn't have "get" in there as that implies we're bumping
the reference count which we don't do at all. We used to but not anmore.
Now we'

file: s/close_fd_get_file()/file_close_fd()/g

That really shouldn't have "get" in there as that implies we're bumping
the reference count which we don't do at all. We used to but not anmore.
Now we're just closing the fd and pick that file from the fdtable
without bumping the reference count. Update the wrong documentation
while at it.

Link: https://lore.kernel.org/r/20231130-vfs-files-fixes-v1-1-e73ca6f4ea83@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>

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Improve __fget_files_rcu() code generation (and thus __fget_light())

Commit 0ede61d8589c ("file: convert to SLAB_TYPESAFE_BY_RCU") caused a
performance regression as reported by the kernel test robo

Improve __fget_files_rcu() code generation (and thus __fget_light())

Commit 0ede61d8589c ("file: convert to SLAB_TYPESAFE_BY_RCU") caused a
performance regression as reported by the kernel test robot.

The __fget_light() function is one of those critical ones for some
loads, and the code generation was unnecessarily impacted. Let's just
write that function to better.

Reported-by: kernel test robot <oliver.sang@intel.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Closes: https://lore.kernel.org/oe-lkp/202311201406.2022ca3f-oliver.sang@intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/CAHk-=wiCJtLbFWNURB34b9a_R_unaH3CiMRXfkR0-iihB_z68A@mail.gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

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file, i915: fix file reference for mmap_singleton()

Today we got a report at [1] for rcu stalls on the i915 testsuite in [2]
due to the conversion of files to SLAB_TYPSSAFE_BY_RCU. Afaict,
get_file_

file, i915: fix file reference for mmap_singleton()

Today we got a report at [1] for rcu stalls on the i915 testsuite in [2]
due to the conversion of files to SLAB_TYPSSAFE_BY_RCU. Afaict,
get_file_rcu() goes into an infinite loop trying to carefully verify
that i915->gem.mmap_singleton hasn't changed - see the splat below.

So I stared at this code to figure out what it actually does. It seems
that the i915->gem.mmap_singleton pointer itself never had rcu semantics.

The i915->gem.mmap_singleton is replaced in
file->f_op->release::singleton_release():

static int singleton_release(struct inode *inode, struct file *file)
{
struct drm_i915_private *i915 = file->private_data;

cmpxchg(&i915->gem.mmap_singleton, file, NULL);
drm_dev_put(&i915->drm);

return 0;
}

The cmpxchg() is ordered against a concurrent update of
i915->gem.mmap_singleton from mmap_singleton(). IOW, when
mmap_singleton() fails to get a reference on i915->gem.mmap_singleton:

While mmap_singleton() does

rcu_read_lock();
file = get_file_rcu(&i915->gem.mmap_singleton);
rcu_read_unlock();

it allocates a new file via anon_inode_getfile() and does

smp_store_mb(i915->gem.mmap_singleton, file);

So, then what happens in the case of this bug is that at some point
fput() is called and drops the file->f_count to zero leaving the pointer
in i915->gem.mmap_singleton in tact.

Now, there might be delays until
file->f_op->release::singleton_release() is called and
i915->gem.mmap_singleton is set to NULL.

Say concurrently another task hits mmap_singleton() and does:

rcu_read_lock();
file = get_file_rcu(&i915->gem.mmap_singleton);
rcu_read_unlock();

When get_file_rcu() fails to get a reference via atomic_inc_not_zero()
it will try the reload from i915->gem.mmap_singleton expecting it to be
NULL, assuming it has comparable semantics as we expect in
__fget_files_rcu().

But it hasn't so it reloads the same pointer again, trying the same
atomic_inc_not_zero() again and doing so until
file->f_op->release::singleton_release() of the old file has been
called.

So, in contrast to __fget_files_rcu() here we want to not retry when
atomic_inc_not_zero() has failed. We only want to retry in case we
managed to get a reference but the pointer did change on reload.

<3> [511.395679] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
<3> [511.395716] rcu: Tasks blocked on level-1 rcu_node (CPUs 0-9): P6238
<3> [511.395934] rcu: (detected by 16, t=65002 jiffies, g=123977, q=439 ncpus=20)
<6> [511.395944] task:i915_selftest state:R running task stack:10568 pid:6238 tgid:6238 ppid:1001 flags:0x00004002
<6> [511.395962] Call Trace:
<6> [511.395966] <TASK>
<6> [511.395974] ? __schedule+0x3a8/0xd70
<6> [511.395995] ? asm_sysvec_apic_timer_interrupt+0x1a/0x20
<6> [511.396003] ? lockdep_hardirqs_on+0xc3/0x140
<6> [511.396013] ? asm_sysvec_apic_timer_interrupt+0x1a/0x20
<6> [511.396029] ? get_file_rcu+0x10/0x30
<6> [511.396039] ? get_file_rcu+0x10/0x30
<6> [511.396046] ? i915_gem_object_mmap+0xbc/0x450 [i915]
<6> [511.396509] ? i915_gem_mmap+0x272/0x480 [i915]
<6> [511.396903] ? mmap_region+0x253/0xb60
<6> [511.396925] ? do_mmap+0x334/0x5c0
<6> [511.396939] ? vm_mmap_pgoff+0x9f/0x1c0
<6> [511.396949] ? rcu_is_watching+0x11/0x50
<6> [511.396962] ? igt_mmap_offset+0xfc/0x110 [i915]
<6> [511.397376] ? __igt_mmap+0xb3/0x570 [i915]
<6> [511.397762] ? igt_mmap+0x11e/0x150 [i915]
<6> [511.398139] ? __trace_bprintk+0x76/0x90
<6> [511.398156] ? __i915_subtests+0xbf/0x240 [i915]
<6> [511.398586] ? __pfx___i915_live_setup+0x10/0x10 [i915]
<6> [511.399001] ? __pfx___i915_live_teardown+0x10/0x10 [i915]
<6> [511.399433] ? __run_selftests+0xbc/0x1a0 [i915]
<6> [511.399875] ? i915_live_selftests+0x4b/0x90 [i915]
<6> [511.400308] ? i915_pci_probe+0x106/0x200 [i915]
<6> [511.400692] ? pci_device_probe+0x95/0x120
<6> [511.400704] ? really_probe+0x164/0x3c0
<6> [511.400715] ? __pfx___driver_attach+0x10/0x10
<6> [511.400722] ? __driver_probe_device+0x73/0x160
<6> [511.400731] ? driver_probe_device+0x19/0xa0
<6> [511.400741] ? __driver_attach+0xb6/0x180
<6> [511.400749] ? __pfx___driver_attach+0x10/0x10
<6> [511.400756] ? bus_for_each_dev+0x77/0xd0
<6> [511.400770] ? bus_add_driver+0x114/0x210
<6> [511.400781] ? driver_register+0x5b/0x110
<6> [511.400791] ? i915_init+0x23/0xc0 [i915]
<6> [511.401153] ? __pfx_i915_init+0x10/0x10 [i915]
<6> [511.401503] ? do_one_initcall+0x57/0x270
<6> [511.401515] ? rcu_is_watching+0x11/0x50
<6> [511.401521] ? kmalloc_trace+0xa3/0xb0
<6> [511.401532] ? do_init_module+0x5f/0x210
<6> [511.401544] ? load_module+0x1d00/0x1f60
<6> [511.401581] ? init_module_from_file+0x86/0xd0
<6> [511.401590] ? init_module_from_file+0x86/0xd0
<6> [511.401613] ? idempotent_init_module+0x17c/0x230
<6> [511.401639] ? __x64_sys_finit_module+0x56/0xb0
<6> [511.401650] ? do_syscall_64+0x3c/0x90
<6> [511.401659] ? entry_SYSCALL_64_after_hwframe+0x6e/0xd8
<6> [511.401684] </TASK>

Link: [1]: https://lore.kernel.org/intel-gfx/SJ1PR11MB6129CB39EED831784C331BAFB9DEA@SJ1PR11MB6129.namprd11.prod.outlook.com
Link: [2]: https://intel-gfx-ci.01.org/tree/linux-next/next-20231013/bat-dg2-11/igt@i915_selftest@live@mman.html#dmesg-warnings10963
Cc: Jann Horn <jannh@google.com>,
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231025-formfrage-watscheln-84526cd3bd7d@brauner
Signed-off-by: Christian Brauner <brauner@kernel.org>

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backing file: free directly

Backing files as used by overlayfs are never installed into file
descriptor tables and are explicitly documented as such. They aren't
subject to rcu access conditions lik

backing file: free directly

Backing files as used by overlayfs are never installed into file
descriptor tables and are explicitly documented as such. They aren't
subject to rcu access conditions like regular files are.

Their lifetime is bound to the lifetime of the overlayfs file, i.e.,
they're stashed in ovl_file->private_data and go away otherwise. If
they're set as vma->vm_file - which is their main purpose - then they're
subject to regular refcount rules and vma->vm_file can't be installed
into an fdtable after having been set. All in all I don't see any need
for rcu delay here. So free it directly.

This all hinges on such hybrid beasts to never actually be installed
into fdtables which - as mentioned before - is not allowed. So add an
explicit WARN_ON_ONCE() so we catch any case where someone is suddenly
trying to install one of those things into a file descriptor table so we
can have a nice long chat with them.

Link: https://lore.kernel.org/r/20231005-sakralbau-wappnen-f5c31755ed70@brauner
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

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file: convert to SLAB_TYPESAFE_BY_RCU

In recent discussions around some performance improvements in the file
handling area we discussed switching the file cache to rely on
SLAB_TYPESAFE_BY_RCU which

file: convert to SLAB_TYPESAFE_BY_RCU

In recent discussions around some performance improvements in the file
handling area we discussed switching the file cache to rely on
SLAB_TYPESAFE_BY_RCU which allows us to get rid of call_rcu() based
freeing for files completely. This is a pretty sensitive change overall
but it might actually be worth doing.

The main downside is the subtlety. The other one is that we should
really wait for Jann's patch to land that enables KASAN to handle
SLAB_TYPESAFE_BY_RCU UAFs. Currently it doesn't but a patch for this
exists.

With SLAB_TYPESAFE_BY_RCU objects may be freed and reused multiple times
which requires a few changes. So it isn't sufficient anymore to just
acquire a reference to the file in question under rcu using
atomic_long_inc_not_zero() since the file might have already been
recycled and someone else might have bumped the reference.

In other words, callers might see reference count bumps from newer
users. For this reason it is necessary to verify that the pointer is the
same before and after the reference count increment. This pattern can be
seen in get_file_rcu() and __files_get_rcu().

In addition, it isn't possible to access or check fields in struct file
without first aqcuiring a reference on it. Not doing that was always
very dodgy and it was only usable for non-pointer data in struct file.
With SLAB_TYPESAFE_BY_RCU it is necessary that callers first acquire a
reference under rcu or they must hold the files_lock of the fdtable.
Failing to do either one of this is a bug.

Thanks to Jann for pointing out that we need to ensure memory ordering
between reallocations and pointer check by ensuring that all subsequent
loads have a dependency on the second load in get_file_rcu() and
providing a fixup that was folded into this patch.

Cc: Jann Horn <jannh@google.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

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fs: Fix kernel-doc warnings

These have a variety of causes and a corresponding variety of solutions.

Signed-off-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Message-Id: <20230818200824.27200

fs: Fix kernel-doc warnings

These have a variety of causes and a corresponding variety of solutions.

Signed-off-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Message-Id: <20230818200824.2720007-1-willy@infradead.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

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fs: rely on ->iterate_shared to determine f_pos locking

Now that we removed ->iterate we don't need to check for either
->iterate or ->iterate_shared in file_needs_f_pos_lock(). Simply check
for ->i

fs: rely on ->iterate_shared to determine f_pos locking

Now that we removed ->iterate we don't need to check for either
->iterate or ->iterate_shared in file_needs_f_pos_lock(). Simply check
for ->iterate_shared instead. This will tell us whether we need to
unconditionally take the lock. Not just does it allow us to avoid
checking f_inode's mode it also actually clearly shows that we're
locking because of readdir.

Signed-off-by: Christian Brauner <brauner@kernel.org>

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file: reinstate f_pos locking optimization for regular files

In commit 20ea1e7d13c1 ("file: always lock position for
FMODE_ATOMIC_POS") we ended up always taking the file pos lock, because
pidfd_get

file: reinstate f_pos locking optimization for regular files

In commit 20ea1e7d13c1 ("file: always lock position for
FMODE_ATOMIC_POS") we ended up always taking the file pos lock, because
pidfd_getfd() could get a reference to the file even when it didn't have
an elevated file count due to threading of other sharing cases.

But Mateusz Guzik reports that the extra locking is actually measurable,
so let's re-introduce the optimization, and only force the locking for
directory traversal.

Directories need the lock for correctness reasons, while regular files
only need it for "POSIX semantics". Since pidfd_getfd() is about
debuggers etc special things that are _way_ outside of POSIX, we can
relax the rules for that case.

Reported-by: Mateusz Guzik <mjguzik@gmail.com>
Cc: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/linux-fsdevel/20230803095311.ijpvhx3fyrbkasul@f/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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file: mostly eliminate spurious relocking in __range_close

Stock code takes a lock trip for every fd in range, but this can be
trivially avoided and real-world consumers do have plenty of already
cl

file: mostly eliminate spurious relocking in __range_close

Stock code takes a lock trip for every fd in range, but this can be
trivially avoided and real-world consumers do have plenty of already
closed cases.

Just booting Debian 12 with a debug printk shows:
(sh) min 3 max 17 closed 15 empty 0
(sh) min 19 max 63 closed 31 empty 14
(sh) min 4 max 63 closed 0 empty 60
(spawn) min 3 max 63 closed 13 empty 48
(spawn) min 3 max 63 closed 13 empty 48
(mount) min 3 max 17 closed 15 empty 0
(mount) min 19 max 63 closed 32 empty 13

and so on.

While here use more idiomatic naming.

An avoidable relock is left in place to avoid uglifying the code.
The code was not switched to bitmap traversal for the same reason.

Tested with ltp kernel/syscalls/close_range

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Message-Id: <20230727113809.800067-1-mjguzik@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

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file: always lock position for FMODE_ATOMIC_POS

The pidfd_getfd() system call allows a caller with ptrace_may_access()
abilities on another process to steal a file descriptor from this
process. This

file: always lock position for FMODE_ATOMIC_POS

The pidfd_getfd() system call allows a caller with ptrace_may_access()
abilities on another process to steal a file descriptor from this
process. This system call is used by debuggers, container runtimes,
system call supervisors, networking proxies etc. So while it is a
special interest system call it is used in common tools.

That ability ends up breaking our long-time optimization in fdget_pos(),
which "knew" that if we had exclusive access to the file descriptor
nobody else could access it, and we didn't need the lock for the file
position.

That check for file_count(file) was always fairly subtle - it depended
on __fdget() not incrementing the file count for single-threaded
processes and thus included that as part of the rule - but it did mean
that we didn't need to take the lock in all those traditional unix
process contexts.

So it's sad to see this go, and I'd love to have some way to re-instate
the optimization. At the same time, the lock obviously isn't ever
contended in the case we optimized, so all we were optimizing away is
the atomics and the cacheline dirtying. Let's see if anybody even
notices that the optimization is gone.

Link: https://lore.kernel.org/linux-fsdevel/20230724-vfs-fdget_pos-v1-1-a4abfd7103f3@kernel.org/
Fixes: 8649c322f75c ("pid: Implement pidfd_getfd syscall")
Cc: stable@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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fs: prevent out-of-bounds array speculation when closing a file descriptor

Google-Bug-Id: 114199369
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs: use acquire ordering in __fget_light()

We must prevent the CPU from reordering the files->count read with the
FD table access like this, on architectures where read-read reordering is
possible:

fs: use acquire ordering in __fget_light()

We must prevent the CPU from reordering the files->count read with the
FD table access like this, on architectures where read-read reordering is
possible:

files_lookup_fd_raw()
close_fd()
put_files_struct()
atomic_read(&files->count)

I would like to mark this for stable, but the stable rules explicitly say
"no theoretical races", and given that the FD table pointer and
files->count are explicitly stored in the same cacheline, this sort of
reordering seems quite unlikely in practice...

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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gfs2: Add glockfd debugfs file

When a process has a gfs2 file open, the file is keeping a reference on the
underlying gfs2 inode, and the inode is keeping the inode's iopen glock held in
shared mode

gfs2: Add glockfd debugfs file

When a process has a gfs2 file open, the file is keeping a reference on the
underlying gfs2 inode, and the inode is keeping the inode's iopen glock held in
shared mode. In other words, the process depends on the iopen glock of each
open gfs2 file. Expose those dependencies in a new "glockfd" debugfs file.

The new debugfs file contains one line for each gfs2 file descriptor,
specifying the tgid, file descriptor number, and glock name, e.g.,

1601 6 5/816d

This list is compiled by iterating all tasks on the system using find_ge_pid(),
and all file descriptors of each task using task_lookup_next_fd_rcu(). To make
that work from gfs2, export those two functions.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

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fix the breakage in close_fd_get_file() calling conventions change

It used to grab an extra reference to struct file rather than
just transferring to caller the one it had removed from descriptor
ta

fix the breakage in close_fd_get_file() calling conventions change

It used to grab an extra reference to struct file rather than
just transferring to caller the one it had removed from descriptor
table. New variant doesn't, and callers need to be adjusted.

Reported-and-tested-by: syzbot+47dd250f527cb7bebf24@syzkaller.appspotmail.com
Fixes: 6319194ec57b ("Unify the primitives for file descriptor closing")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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Unify the primitives for file descriptor closing

Currently we have 3 primitives for removing an opened file from descriptor
table - pick_file(), __close_fd_get_file() and close_fd_get_file(). Their

Unify the primitives for file descriptor closing

Currently we have 3 primitives for removing an opened file from descriptor
table - pick_file(), __close_fd_get_file() and close_fd_get_file(). Their
calling conventions are rather odd and there's a code duplication for no
good reason. They can be unified -

1) have __range_close() cap max_fd in the very beginning; that way
we don't need separate way for pick_file() to report being past the end
of descriptor table.

2) make {__,}close_fd_get_file() return file (or NULL) directly, rather
than returning it via struct file ** argument. Don't bother with
(bogus) return value - nobody wants that -ENOENT.

3) make pick_file() return NULL on unopened descriptor - the only caller
that used to care about the distinction between descriptor past the end
of descriptor table and finding NULL in descriptor table doesn't give
a damn after (1).

4) lift ->files_lock out of pick_file()

That actually simplifies the callers, as well as the primitives themselves.
Code duplication is also gone...

Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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