On Thu, Nov 17, 2022 at 09:38:54PM +0800, Long Li wrote:
> The following error occurred during the fsstress test:
>
> XFS: Assertion failed: VFS_I(ip)->i_nlink >= 2, file: fs/xfs/xfs_inode.c, line: 2452
>
> 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
>
> xfs_reinit_inode() needs to hold the ILOCK_EXCL as it is changing internal
> inode state and can race with other RCU protected inode lookups. On the
> read side, xfs_iflush_cluster() grabs the ILOCK_SHARED while under rcu +
> ip->i_flags_lock, and so xfs_iflush/xfs_inode_to_disk() are protected from
> racing inode updates (during transactions) by that lock.
>
> Signed-off-by: Long Li <leo.lilong@xxxxxxxxxx>
> ---
> v2:
> - Modify the assertion error code line number
> - Use ILOCK_EXCL to prevent inode racing
> v3:
> - Put ilock and iunlock in the same function
Thanks for fixing that, I'll run this through testing overnight.
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
>
> fs/xfs/xfs_icache.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index eae7427062cf..f35e2cee5265 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
> @@ -342,6 +342,9 @@ xfs_iget_recycle(
>
> trace_xfs_iget_recycle(ip);
>
> + if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL))
> + return -EAGAIN;
> +
> /*
> * We need to make it look like the inode is being reclaimed to prevent
> * the actual reclaim workers from stomping over us while we recycle
> @@ -355,6 +358,7 @@ xfs_iget_recycle(
>
> ASSERT(!rwsem_is_locked(&inode->i_rwsem));
> error = xfs_reinit_inode(mp, inode);
> + xfs_iunlock(ip, XFS_ILOCK_EXCL);
> if (error) {
> /*
> * Re-initializing the inode failed, and we are in deep
> @@ -518,6 +522,8 @@ xfs_iget_cache_hit(
> if (ip->i_flags & XFS_IRECLAIMABLE) {
> /* Drops i_flags_lock and RCU read lock. */
> error = xfs_iget_recycle(pag, ip);
> + if (error == -EAGAIN)
> + goto out_skip;
> if (error)
> return error;
> } else {
> --
> 2.31.1
>
