[PATCH v2 3/3] block: Preserve LBA order when requeuing

[Bart Van Assche <bvanassche@xxxxxxx>]

When requeuing a request to a zoned block device, preserve the LBA order
per zone.

Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
Cc: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
 block/blk-mq.c | 45 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 39 insertions(+), 6 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index cc32ad0cd548..2ec7d6140114 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1495,6 +1495,44 @@ static void blk_mq_requeue_work(struct work_struct *work)
 	blk_mq_run_hw_queues(q, false);
 }
 
+static void blk_mq_insert_rq(struct request *rq, struct list_head *list,
+			     bool at_head)
+{
+	bool zone_in_list = false;
+	struct request *rq2;
+
+	/*
+	 * For request queues associated with a zoned block device, check
+	 * whether another request for the same zone has already been queued.
+	 */
+	if (blk_queue_is_zoned(rq->q)) {
+		const unsigned int zno = blk_rq_zone_no(rq);
+
+		list_for_each_entry(rq2, list, queuelist) {
+			if (blk_rq_zone_no(rq2) == zno) {
+				zone_in_list = true;
+				if (blk_rq_pos(rq) < blk_rq_pos(rq2))
+					break;
+			}
+		}
+	}
+	if (!zone_in_list) {
+		if (at_head) {
+			rq->rq_flags |= RQF_SOFTBARRIER;
+			list_add(&rq->queuelist, list);
+		} else {
+			list_add_tail(&rq->queuelist, list);
+		}
+	} else {
+		/*
+		 * Insert the request in the list before another request for
+		 * the same zone and with a higher LBA. If there is no such
+		 * request, insert the request at the end of the list.
+		 */
+		list_add_tail(&rq->queuelist, &rq2->queuelist);
+	}
+}
+
 void blk_mq_add_to_requeue_list(struct request *rq, bool at_head,
 				bool kick_requeue_list)
 {
@@ -1508,12 +1546,7 @@ void blk_mq_add_to_requeue_list(struct request *rq, bool at_head,
 	BUG_ON(rq->rq_flags & RQF_SOFTBARRIER);
 
 	spin_lock_irqsave(&q->requeue_lock, flags);
-	if (at_head) {
-		rq->rq_flags |= RQF_SOFTBARRIER;
-		list_add(&rq->queuelist, &q->requeue_list);
-	} else {
-		list_add_tail(&rq->queuelist, &q->requeue_list);
-	}
+	blk_mq_insert_rq(rq, &q->requeue_list, at_head);
 	spin_unlock_irqrestore(&q->requeue_lock, flags);
 
 	if (kick_requeue_list)