Re: [PATCH V2 1/2] block: fix race between adding/removing rq qos and normal IO

 static inline void rq_qos_add(struct request_queue *q, struct rq_qos *rqos)
 {
+	/*
+	 * No IO can be in-flight when adding rqos, so freeze queue, which
+	 * is fine since we only support rq_qos for blk-mq queue
+	 */
+	blk_mq_freeze_queue(q);
 	rqos->next = q->rq_qos;
 	q->rq_qos = rqos;
+	blk_mq_unfreeze_queue(q);
 
 	if (rqos->ops->debugfs_attrs)
 		blk_mq_debugfs_register_rqos(rqos);

@@ -110,12 +117,18 @@ static inline void rq_qos_del(struct request_queue *q, struct rq_qos *rqos)
 {
 	struct rq_qos **cur;
 
+	/*
+	 * No IO can be in-flight when removing rqos, so freeze queue,
+	 * which is fine since we only support rq_qos for blk-mq queue
+	 */
+	blk_mq_freeze_queue(q);
 	for (cur = &q->rq_qos; *cur; cur = &(*cur)->next) {
 		if (*cur == rqos) {
 			*cur = rqos->next;
 			break;
 		}
 	}
+	blk_mq_unfreeze_queue(q);
 
 	blk_mq_debugfs_unregister_rqos(rqos);
 }