1 files changed, 7 insertions, 0 deletions
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index b9f4cc4..28d227c 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -872,6 +872,13 @@ void blkcg_drain_queue(struct request_queue *q)
 {
 	lockdep_assert_held(q->queue_lock);
 
+	/*
+	 * @q could be exiting and already have destroyed all blkgs as
+	 * indicated by NULL root_blkg.  If so, don't confuse policies.
+	 */
+	if (!q->root_blkg)
+		return;
+
 	blk_throtl_drain(q);
 }