block: Cleanup elevator_init_mq() use

Instead of checking a queue tag_set BLK_MQ_F_NO_SCHED flag before
calling elevator_init_mq() to make sure that the queue supports IO
scheduling, use the elevator.c function elv_support_iosched() in
elevator_init_mq(). This does not introduce any functional change but
ensure that elevator_init_mq() does the right thing based on the queue
settings.
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -2910,11 +2910,9 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 	blk_mq_add_queue_tag_set(set, q);
 	blk_mq_map_swqueue(q);
 
-	if (!(set->flags & BLK_MQ_F_NO_SCHED)) {
-		ret = elevator_init_mq(q);
-		if (ret)
-			goto err_tag_set;
-	}
+	ret = elevator_init_mq(q);
+	if (ret)
+		goto err_tag_set;
 
 	return q;
 

block/elevator.c

@@ -619,16 +619,26 @@ int elevator_switch_mq(struct request_queue *q,
 	return ret;
 }
 
+static inline bool elv_support_iosched(struct request_queue *q)
+{
+	if (q->tag_set && (q->tag_set->flags & BLK_MQ_F_NO_SCHED))
+		return false;
+	return true;
+}
+
 /*
- * For blk-mq devices, we default to using mq-deadline, if available, for single
- * queue devices.  If deadline isn't available OR we have multiple queues,
- * default to "none".
+ * For blk-mq devices supporting IO scheduling, we default to using mq-deadline,
+ * if available, for single queue devices. If deadline isn't available OR we
+ * have multiple queues, default to "none".
  */
 int elevator_init_mq(struct request_queue *q)
 {
 	struct elevator_type *e;
 	int err = 0;
 
+	if (!elv_support_iosched(q))
+		return 0;
+
 	if (q->nr_hw_queues != 1)
 		return 0;
 
@@ -706,13 +716,6 @@ static int __elevator_change(struct request_queue *q, const char *name)
 	return elevator_switch(q, e);
 }
 
-static inline bool elv_support_iosched(struct request_queue *q)
-{
-	if (q->tag_set && (q->tag_set->flags & BLK_MQ_F_NO_SCHED))
-		return false;
-	return true;
-}
-
 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
 			  size_t count)
 {