In blk_mq_update_nr_hw_queues(), debugfs_mutex is not held while
creating debugfs entries for hctxs. Hence add debugfs_mutex there,
it's safe because queue is not frozen.

Signed-off-by: Yu Kuai <yukuai@fnnas.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
---
 block/blk-mq-debugfs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 22c182b40bc3..5c7cadf51a88 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -679,8 +679,10 @@ void blk_mq_debugfs_register_hctxs(struct request_queue *q)
 	struct blk_mq_hw_ctx *hctx;
 	unsigned long i;
 
+	mutex_lock(&q->debugfs_mutex);
 	queue_for_each_hw_ctx(q, hctx, i)
 		blk_mq_debugfs_register_hctx(q, hctx);
+	mutex_unlock(&q->debugfs_mutex);
 }
 
 void blk_mq_debugfs_unregister_hctxs(struct request_queue *q)
-- 
2.51.0