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cifs: add cifs_resize_file_locked() to guard fscache_resize_cookie() under i_rwsem

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cifs_setsize() calls fscache_resize_cookie() without holding i_rwsem.
When the fscache cookie is active (FSCACHE_COOKIE_IS_CACHING is set),
fscache_resize_cookie() performs a real resize that requires i_rwsem
held exclusively.  If another file descriptor has the same inode open,
fscache_use_cookie() was already called from that cifs_open(), making
the cookie active.  In that case, calling cifs_setsize() from
cifs_do_truncate() (invoked from cifs_open() without i_rwsem) races
against concurrent fscache I/O.

Strip fscache_resize_cookie() from cifs_setsize(), making it a pure
size/page-cache helper.  Add cifs_resize_file_locked() for callers
that already hold i_rwsem: it calls netfs_resize_file() and
cifs_setsize(), then temporarily activates the cookie with
fscache_use_cookie() to perform the resize under the lock, then
deactivates it with cifs_fscache_unuse_inode_cookie().  Using
fscache_use_cookie() before the resize ensures correctness whether or
not another fd already holds the cookie active.

Switch cifs_file_set_size(), smb2_duplicate_extents(), and both size-
extension branches of smb3_simple_falloc() to the new wrapper; those
paths already hold i_rwsem via VFS setattr, lock_two_nondirectories(),
or cifs_fallocate() respectively.  cifs_do_truncate() continues to
call cifs_setsize() followed by cifs_invalidate_cache(), since it runs
without i_rwsem.

Fixes: fa724e235c ("cifs: add fscache_resize_cookie() to cifs_setsize()")
Cc: stable@vger.kernel.org
Cc: David Howells <dhowells@redhat.com>
Cc: Paulo Alcantara <pc@manguebit.com>
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
This commit is contained in:
Frank Sorenson 2026-07-31 12:12:29 -05:00 • committed by Paulo Alcantara
commit 32a7af68df
3 changed files with 23 additions and 11 deletions
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