xfs: add log item pinning error injection tag

Add an error injection tag to force log items in the AIL to the
pinned state. This option can be used by test infrastructure to
induce head behind tail conditions. Specifically, this is intended
to be used by xfstests to reproduce log recovery problems after
failed/corrupted log writes overwrite the last good tail LSN in the
log.

When enabled, AIL push attempts see log items in the AIL in the
pinned state. This stalls metadata writeback and thus prevents the
current tail of the log from moving forward. When disabled,
subsequent AIL pushes observe the log items in their appropriate
state and filesystem operation continues as normal.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 16 insertions, 1 deletions

diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
index 70f5ab017323..354368a906e5 100644
--- a/fs/xfs/xfs_trans_ail.c
+++ b/fs/xfs/xfs_trans_ail.c
@@ -325,6 +325,21 @@ xfs_ail_delete(
 	xfs_trans_ail_cursor_clear(ailp, lip);
 }
 
+static inline uint
+xfsaild_push_item(
+	struct xfs_ail		*ailp,
+	struct xfs_log_item	*lip)
+{
+	/*
+	 * If log item pinning is enabled, skip the push and track the item as
+	 * pinned. This can help induce head-behind-tail conditions.
+	 */
+	if (XFS_TEST_ERROR(false, ailp->xa_mount, XFS_ERRTAG_LOG_ITEM_PIN))
+		return XFS_ITEM_PINNED;
+
+	return lip->li_ops->iop_push(lip, &ailp->xa_buf_list);
+}
+
 static long
 xfsaild_push(
 	struct xfs_ail		*ailp)
@@ -382,7 +397,7 @@ xfsaild_push(
 		 * rely on the AIL cursor implementation to be able to deal with
 		 * the dropped lock.
 		 */
-		lock_result = lip->li_ops->iop_push(lip, &ailp->xa_buf_list);
+		lock_result = xfsaild_push_item(ailp, lip);
 		switch (lock_result) {
 		case XFS_ITEM_SUCCESS:
 			XFS_STATS_INC(mp, xs_push_ail_success);