1 files changed, 9 insertions, 6 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 83930f65016a..af42efbb0c1d 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -213,7 +213,7 @@ void blkiocg_update_avg_queue_size_stats(struct blkio_group *blkg)
 }
 EXPORT_SYMBOL_GPL(blkiocg_update_avg_queue_size_stats);
 
-void blkiocg_set_start_empty_time(struct blkio_group *blkg, bool ignore)
+void blkiocg_set_start_empty_time(struct blkio_group *blkg)
 {
         unsigned long flags;
         struct blkio_group_stats *stats;
@@ -228,12 +228,15 @@ void blkiocg_set_start_empty_time(struct blkio_group *blkg, bool ignore)
         }
 
         /*
-         * If ignore is set, we do not panic on the empty flag being set
-         * already. This is to avoid cases where there are superfluous timeslice
-         * complete events (for eg., forced_dispatch in CFQ) when no IOs are
-         * served which could result in triggering the empty check incorrectly.
+         * group is already marked empty. This can happen if cfqq got new
+         * request in parent group and moved to this group while being added
+         * to service tree. Just ignore the event and move on.
          */
-        BUG_ON(!ignore && blkio_blkg_empty(stats));
+        if(blkio_blkg_empty(stats)) {
+                spin_unlock_irqrestore(&blkg->stats_lock, flags);
+                return;
+        }
+
         stats->start_empty_time = sched_clock();
         blkio_mark_blkg_empty(stats);
         spin_unlock_irqrestore(&blkg->stats_lock, flags);