linux-kernel - [PATCH AUTOSEL 5.10 13/18] blk-mq: don't grab rq's refcount in blk_mq_check

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Message-Id: <20210824005432.631154-13-sashal@kernel.org>
Date:   Mon, 23 Aug 2021 20:54:27 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Ming Lei <ming.lei@...hat.com>, Keith Busch <kbusch@...nel.org>,
        Christoph Hellwig <hch@....de>,
        John Garry <john.garry@...wei.com>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>,
        linux-block@...r.kernel.org
Subject: [PATCH AUTOSEL 5.10 13/18] blk-mq: don't grab rq's refcount in blk_mq_check_expired()

From: Ming Lei <ming.lei@...hat.com>

[ Upstream commit c797b40ccc340b8a66f7a7842aecc90bf749f087 ]

Inside blk_mq_queue_tag_busy_iter() we already grabbed request's
refcount before calling ->fn(), so needn't to grab it one more time
in blk_mq_check_expired().

Meantime remove extra request expire check in blk_mq_check_expired().

Cc: Keith Busch <kbusch@...nel.org>
Signed-off-by: Ming Lei <ming.lei@...hat.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: John Garry <john.garry@...wei.com>
Link: https://lore.kernel.org/r/20210811155202.629575-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 block/blk-mq.c | 30 +++++-------------------------
 1 file changed, 5 insertions(+), 25 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index a368eb6dc647..044d0e3a15ad 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -941,34 +941,14 @@ static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
 	unsigned long *next = priv;
 
 	/*
-	 * Just do a quick check if it is expired before locking the request in
-	 * so we're not unnecessarilly synchronizing across CPUs.
-	 */
-	if (!blk_mq_req_expired(rq, next))
-		return true;
-
-	/*
-	 * We have reason to believe the request may be expired. Take a
-	 * reference on the request to lock this request lifetime into its
-	 * currently allocated context to prevent it from being reallocated in
-	 * the event the completion by-passes this timeout handler.
-	 *
-	 * If the reference was already released, then the driver beat the
-	 * timeout handler to posting a natural completion.
-	 */
-	if (!refcount_inc_not_zero(&rq->ref))
-		return true;
-
-	/*
-	 * The request is now locked and cannot be reallocated underneath the
-	 * timeout handler's processing. Re-verify this exact request is truly
-	 * expired; if it is not expired, then the request was completed and
-	 * reallocated as a new request.
+	 * blk_mq_queue_tag_busy_iter() has locked the request, so it cannot
+	 * be reallocated underneath the timeout handler's processing, then
+	 * the expire check is reliable. If the request is not expired, then
+	 * it was completed and reallocated as a new request after returning
+	 * from blk_mq_check_expired().
 	 */
 	if (blk_mq_req_expired(rq, next))
 		blk_mq_rq_timed_out(rq, reserved);
-
-	blk_mq_put_rq_ref(rq);
 	return true;
 }
 
-- 
2.30.2