[PATCH] xfs: fix incorrect i_nlink caused by inode racing

Long Li
2022-11-07T14:15:18Z

The following error occurred during the fsstress test:

XFS: Assertion failed: VFS_I(ip)->i_nlink >= 2, file: fs/xfs/xfs_inode.c, line: 2925

The problem was that inode race condition causes incorrect i_nlink to be
written to disk, and then it is read into memory. Consider the following
call graph, inodes that are marked as both XFS_IFLUSHING and
XFS_IRECLAIMABLE, i_nlink will be reset to 1 and then restored to original
value in xfs_reinit_inode(). Therefore, the i_nlink of directory on disk
may be set to 1.

xfsaild
xfs_inode_item_push
xfs_iflush_cluster
xfs_iflush
xfs_inode_to_disk

xfs_iget
xfs_iget_cache_hit
xfs_iget_recycle
xfs_reinit_inode
inode_init_always

So skip inodes that being flushed and markded as XFS_IRECLAIMABLE, prevent
concurrent read and write to inodes.

Signed-off-by: Long Li <leo.lilong@huawei.com>
---
fs/xfs/xfs_icache.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index eae7427062cf..cc68b0ff50ce 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -514,6 +514,11 @@ xfs_iget_cache_hit(
(ip->i_flags & XFS_IRECLAIMABLE))
goto out_skip;

+ /* Skip inodes that being flushed */
+ if ((ip->i_flags & XFS_IFLUSHING) &&
+ (ip->i_flags & XFS_IRECLAIMABLE))
+ goto out_skip;
+
/* The inode fits the selection criteria; process it. */
if (ip->i_flags & XFS_IRECLAIMABLE) {
/* Drops i_flags_lock and RCU read lock. */
--
2.31.1