linux-kernel - [PATCH v3 12/14] blk-mq: remove set of bd->last when get driver tag for next request fails

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Date:   Wed, 11 Jan 2023 21:01:57 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     hch@....de, axboe@...nel.dk, dwagner@...e.de, hare@...e.de,
        ming.lei@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     john.garry@...wei.com, jack@...e.cz
Subject: [PATCH v3 12/14] blk-mq: remove set of bd->last when get driver tag for next request fails

Commit 113285b473824 ("blk-mq: ensure that bd->last is always set
correctly") will set last if we failed to get driver tag for next
request to avoid flush miss as we break the list walk and will not
send the last request in the list which will be sent with last set
normally.
This code seems stale now becase the flush introduced is always
redundant as:
For case tag is really out, we will send a extra flush if we find
list is not empty after list walk.
For case some tag is freed before retry in blk_mq_prep_dispatch_rq for
next, then we can get a tag for next request in retry and flush notified
already is not necessary.

Just remove these stale codes.

Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
---
 block/blk-mq.c | 24 ++----------------------
 1 file changed, 2 insertions(+), 22 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index b2133af1c846..1b66a5169be2 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1923,16 +1923,6 @@ static void blk_mq_update_dispatch_busy(struct blk_mq_hw_ctx *hctx, bool busy)
 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);
 }
@@ -2038,7 +2028,7 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 {
 	enum prep_dispatch prep;
 	struct request_queue *q = hctx->queue;
-	struct request *rq, *nxt;
+	struct request *rq;
 	int queued;
 	blk_status_t ret = BLK_STS_OK;
 	LIST_HEAD(zone_list);
@@ -2064,17 +2054,7 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 		list_del_init(&rq->queuelist);
 
 		bd.rq = rq;
-
-		/*
-		 * Flag last if we have no more requests, or if we have more
-		 * but can't assign a driver tag to it.
-		 */
-		if (list_empty(list))
-			bd.last = true;
-		else {
-			nxt = list_first_entry(list, struct request, queuelist);
-			bd.last = !blk_mq_get_driver_tag(nxt);
-		}
+		bd.last = list_empty(list);
 
 		/*
 		 * once the request is queued to lld, no need to cover the
-- 
2.30.0