X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=block%2Fblk-cgroup.c;h=1ff8e97f853ad719ee13994f0d5fc3fafb76a775;hb=b5e10b06c525414503cd40b536604b0167c062e6;hp=e8918ffaf96d4a0a2dacf75838b5d8a89e5e8ca3;hpb=0faa3146f17295f612abadafbfe3d4346178f10f;p=firefly-linux-kernel-4.4.55.git

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index e8918ffaf96d..1ff8e97f853a 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -876,6 +876,20 @@ 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;
+
+	/*
+	 * @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);
 }