1 files changed, 29 insertions, 38 deletions

diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
index 43233e9..c15aa29 100644
--- a/fs/xfs/xfs_trans_ail.c
+++ b/fs/xfs/xfs_trans_ail.c
@@ -299,7 +299,7 @@ xfs_trans_ail_cursor_last(
  * Splice the log item list into the AIL at the given LSN. We splice to the
  * tail of the given LSN to maintain insert order for push traversals. The
  * cursor is optional, allowing repeated updates to the same LSN to avoid
- * repeated traversals.
+ * repeated traversals.  This should not be called with an empty list.
  */
 static void
 xfs_ail_splice(
@@ -308,50 +308,39 @@ xfs_ail_splice(
 	struct list_head	*list,
 	xfs_lsn_t		lsn)
 {
-	struct xfs_log_item	*lip = cur ? cur->item : NULL;
-	struct xfs_log_item	*next_lip;
+	struct xfs_log_item	*lip;
+
+	ASSERT(!list_empty(list));
 
 	/*
-	 * Get a new cursor if we don't have a placeholder or the existing one
-	 * has been invalidated.
+	 * Use the cursor to determine the insertion point if one is
+	 * provided.  If not, or if the one we got is not valid,
+	 * find the place in the AIL where the items belong.
 	 */
-	if (!lip || (__psint_t)lip & 1) {
+	lip = cur ? cur->item : NULL;
+	if (!lip || (__psint_t) lip & 1)
 		lip = __xfs_trans_ail_cursor_last(ailp, lsn);
 
-		if (!lip) {
-			/* The list is empty, so just splice and return.  */
-			if (cur)
-				cur->item = NULL;
-			list_splice(list, &ailp->xa_ail);
-			return;
-		}
-	}
+	/*
+	 * If a cursor is provided, we know we're processing the AIL
+	 * in lsn order, and future items to be spliced in will
+	 * follow the last one being inserted now.  Update the
+	 * cursor to point to that last item, now while we have a
+	 * reliable pointer to it.
+	 */
+	if (cur)
+		cur->item = list_entry(list->prev, struct xfs_log_item, li_ail);
 
 	/*
-	 * Our cursor points to the item we want to insert _after_, so we have
-	 * to update the cursor to point to the end of the list we are splicing
-	 * in so that it points to the correct location for the next splice.
-	 * i.e. before the splice
-	 *
-	 *  lsn -> lsn -> lsn + x -> lsn + x ...
-	 *          ^
-	 *          | cursor points here
-	 *
-	 * After the splice we have:
-	 *
-	 *  lsn -> lsn -> lsn -> lsn -> .... -> lsn -> lsn + x -> lsn + x ...
-	 *          ^                            ^
-	 *          | cursor points here         | needs to move here
-	 *
-	 * So we set the cursor to the last item in the list to be spliced
-	 * before we execute the splice, resulting in the cursor pointing to
-	 * the correct item after the splice occurs.
+	 * Finally perform the splice.  Unless the AIL was empty,
+	 * lip points to the item in the AIL _after_ which the new
+	 * items should go.  If lip is null the AIL was empty, so
+	 * the new items go at the head of the AIL.
 	 */
-	if (cur) {
-		next_lip = list_entry(list->prev, struct xfs_log_item, li_ail);
-		cur->item = next_lip;
-	}
-	list_splice(list, &lip->li_ail);
+	if (lip)
+		list_splice(list, &lip->li_ail);
+	else
+		list_splice(list, &ailp->xa_ail);
 }
 
 /*
@@ -682,6 +671,7 @@ xfs_trans_ail_update_bulk(
 	int			i;
 	LIST_HEAD(tmp);
 
+	ASSERT(nr_items > 0);		/* Not required, but true. */
 	mlip = xfs_ail_min(ailp);
 
 	for (i = 0; i < nr_items; i++) {
@@ -701,7 +691,8 @@ xfs_trans_ail_update_bulk(
 		list_add(&lip->li_ail, &tmp);
 	}
 
-	xfs_ail_splice(ailp, cur, &tmp, lsn);
+	if (!list_empty(&tmp))
+		xfs_ail_splice(ailp, cur, &tmp, lsn);
 
 	if (!mlip_changed) {
 		spin_unlock(&ailp->xa_lock);