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xfs: fix locking in xchk_nlinks_collect_dir

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On a filesystem with parent pointers, xchk_nlinks_collect_dir walks both
the directory entries (data fork) and the parent pointers (attr fork) to
determine the correct link count.  Unfortunately I forgot to update the
lock mode logic to handle the case of a directory whose attr fork is in
btree format and has not yet been loaded *and* whose data fork doesn't
need loading.

This leads to a bunch of assertions from xfs/286 in xfs_iread_extents
because we only took ILOCK_SHARED, not ILOCK_EXCL.  You'd need the rare
happenstance of a directory with a large number of non-pptr extended
attributes set and enough memory pressure to cause the directory to be
evicted and partially reloaded from disk.

I /think/ this only started in 6.18-rc1 because I've started seeing OOM
errors with the maple tree slab using 70% of memory, and this didn't
happen in 6.17.  Yay dynamic systems!

Cc: stable@vger.kernel.org # v6.10
Fixes: 77ede5f44b ("xfs: walk directory parent pointers to determine backref count")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
This commit is contained in:
Darrick J. Wong
2025-10-21 11:30:43 -07:00
committed by Carlos Maiolino
parent 3e7ec343f0
commit f477af0cfa
1 changed files with 31 additions and 3 deletions
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34
fs/xfs/scrub/nlinks.c
View File

@@ -376,6 +376,36 @@ out_incomplete:
return error;
}
static uint
xchk_nlinks_ilock_dir(
struct xfs_inode *ip)
{
uint lock_mode = XFS_ILOCK_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.
*/
if (xfs_need_iread_extents(&ip->i_df))
lock_mode = XFS_ILOCK_EXCL;
/*
* We're going to scan the parent pointers, so we must be ready to
* pull the attr fork mappings into memory if they aren't already.
*/
if (xfs_has_parent(ip->i_mount) && xfs_inode_has_attr_fork(ip) &&
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;
}
/* Walk a directory to bump the observed link counts of the children. */
STATIC int
xchk_nlinks_collect_dir(
@@ -394,8 +424,7 @@ xchk_nlinks_collect_dir(
return 0;
/* Prevent anyone from changing this directory while we walk it. */
xfs_ilock(dp, XFS_IOLOCK_SHARED);
lock_mode = xfs_ilock_data_map_shared(dp);
lock_mode = xchk_nlinks_ilock_dir(dp);
/*
* The dotdot entry of an unlinked directory still points to the last
@@ -452,7 +481,6 @@ out_abort:
xchk_iscan_abort(&xnc->collect_iscan);
out_unlock:
xfs_iunlock(dp, lock_mode);
xfs_iunlock(dp, XFS_IOLOCK_SHARED);
return error;
}