1 files changed, 29 insertions, 38 deletions

diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
index 43233e92f0f6..c15aa29fa169 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);