block: factor out requeue handling from dispatch code

Factor out the requeue handling from the dispatch code, this will make
subsequent addition of different requeueing schemes easier.
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -1178,6 +1178,23 @@ static void blk_mq_update_dispatch_busy(struct blk_mq_hw_ctx *hctx, bool busy)
 
 #define BLK_MQ_RESOURCE_DELAY	3		/* ms units */
 
+static void blk_mq_handle_dev_resource(struct request *rq,
+				       struct list_head *list)
+{
+	struct request *next =
+		list_first_entry_or_null(list, struct request, queuelist);
+
+	/*
+	 * If an I/O scheduler has been configured and we got a driver tag for
+	 * the next request already, free it.
+	 */
+	if (next)
+		blk_mq_put_driver_tag(next);
+
+	list_add(&rq->queuelist, list);
+	__blk_mq_requeue_request(rq);
+}
+
 /*
  * Returns true if we did some work AND can potentially do more.
  */
@@ -1245,17 +1262,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
 
 		ret = q->mq_ops->queue_rq(hctx, &bd);
 		if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE) {
-			/*
-			 * If an I/O scheduler has been configured and we got a
-			 * driver tag for the next request already, free it
-			 * again.
-			 */
-			if (!list_empty(list)) {
-				nxt = list_first_entry(list, struct request, queuelist);
-				blk_mq_put_driver_tag(nxt);
-			}
-			list_add(&rq->queuelist, list);
-			__blk_mq_requeue_request(rq);
+			blk_mq_handle_dev_resource(rq, list);
 			break;
 		}