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xfs: nlink scrub must take IOLOCK before determining ILOCK state

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In xchk_nlinks_ilock_dir, take the IOLOCK before accessing internal
inode state to figure out if we need to take ILOCK shared or exclusive.
That way we can't race with directory updates.  LOLLM pointed out that
the code was initially correct w.r.t. the IOLOCK, but then I broke it.

Cc: stable@vger.kernel.org # v6.18
Fixes: f477af0cfa ("xfs: fix locking in xchk_nlinks_collect_dir")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Assisted-by: LOLLM # finding obvious bugs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
This commit is contained in:
Darrick J. Wong
2026-07-26 22:24:02 -07:00
committed by Carlos Maiolino
parent 5ee37132ea
commit b1a296fc22
1 changed files with 7 additions and 6 deletions
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13
fs/xfs/scrub/nlinks.c
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@@ -382,6 +382,12 @@ xchk_nlinks_ilock_dir(
{
uint lock_mode = XFS_ILOCK_SHARED;
/*
* Take the IOLOCK so that other threads cannot start a directory
* update while we're scanning.
*/
xfs_ilock(ip, XFS_IOLOCK_SHARED);
/*
* We're going to scan the directory entries, so we must be ready to
* pull the data fork mappings into memory if they aren't already.
@@ -397,13 +403,8 @@ xchk_nlinks_ilock_dir(
xfs_need_iread_extents(&ip->i_af))
lock_mode = XFS_ILOCK_EXCL;
/*
* Take the IOLOCK so that other threads cannot start a directory
* update while we're scanning.
*/
lock_mode |= XFS_IOLOCK_SHARED;
xfs_ilock(ip, lock_mode);
return lock_mode;
return lock_mode | XFS_IOLOCK_SHARED;
}
/* Walk a directory to bump the observed link counts of the children. */