block: mq-deadline: Reduce lock contention

blk_mq_free_requests() calls dd_finish_request() indirectly. Prevent
nested locking of dd->lock and dd->zone_lock by moving the code for
freeing requests.
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230517174230.897144-9-bvanassche@acm.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/mq-deadline.c

@@ -757,7 +757,7 @@ static bool dd_bio_merge(struct request_queue *q, struct bio *bio,
  * add rq to rbtree and fifo
  */
 static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
-			      blk_insert_t flags)
+			      blk_insert_t flags, struct list_head *free)
 {
 	struct request_queue *q = hctx->queue;
 	struct deadline_data *dd = q->elevator->elevator_data;
@@ -766,7 +766,6 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
 	u8 ioprio_class = IOPRIO_PRIO_CLASS(ioprio);
 	struct dd_per_prio *per_prio;
 	enum dd_prio prio;
-	LIST_HEAD(free);
 
 	lockdep_assert_held(&dd->lock);
 
@@ -783,10 +782,8 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
 		rq->elv.priv[0] = (void *)(uintptr_t)1;
 	}
 
-	if (blk_mq_sched_try_insert_merge(q, rq, &free)) {
-		blk_mq_free_requests(&free);
+	if (blk_mq_sched_try_insert_merge(q, rq, free))
 		return;
-	}
 
 	trace_block_rq_insert(rq);
 
@@ -819,6 +816,7 @@ static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
 {
 	struct request_queue *q = hctx->queue;
 	struct deadline_data *dd = q->elevator->elevator_data;
+	LIST_HEAD(free);
 
 	spin_lock(&dd->lock);
 	while (!list_empty(list)) {
@@ -826,9 +824,11 @@ static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
 
 		rq = list_first_entry(list, struct request, queuelist);
 		list_del_init(&rq->queuelist);
-		dd_insert_request(hctx, rq, flags);
+		dd_insert_request(hctx, rq, flags, &free);
 	}
 	spin_unlock(&dd->lock);
+
+	blk_mq_free_requests(&free);
 }
 
 /* Callback from inside blk_mq_rq_ctx_init(). */