linux-kernel - [PATCH 2/2] blk-mq: remove unnecessary blk_clear_rq

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Date:	Wed, 17 Sep 2014 17:47:58 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org
Cc:	Christoph Hellwig <hch@....de>, Ming Lei <ming.lei@...oical.com>
Subject: [PATCH 2/2] blk-mq: remove unnecessary blk_clear_rq_complete()

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

This patch removes two unnecessary blk_clear_rq_complete(),
the REQ_ATOM_COMPLETE flag is cleared inside blk_mq_start_request(),
so:

	- The blk_clear_rq_complete() in blk_flush_restore_request()
	needn't because the request will be freed later, and clearing
	it here may open a small race window with timeout.

	- The blk_clear_rq_complete() in blk_mq_requeue_request() isn't
	necessary too, even though REQ_ATOM_STARTED is cleared in
	__blk_mq_requeue_request(), in theory it still may cause a small
	race window with timeout since the two clear_bit() may be
	reordered.

Signed-off-by: Ming Lei <ming.lei@...oical.com>
---
 block/blk-flush.c |    2 --
 block/blk-mq.c    |    1 -
 2 files changed, 3 deletions(-)

diff --git a/block/blk-flush.c b/block/blk-flush.c
index b439670..db6dfb4 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -127,8 +127,6 @@ static void blk_flush_restore_request(struct request *rq)
 	/* make @rq a normal request */
 	rq->cmd_flags &= ~REQ_FLUSH_SEQ;
 	rq->end_io = rq->flush.saved_end_io;
-
-	blk_clear_rq_complete(rq);
 }
 
 static bool blk_flush_queue_rq(struct request *rq, bool add_front)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 957815e..6e4942d 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -430,7 +430,6 @@ static void __blk_mq_requeue_request(struct request *rq)
 void blk_mq_requeue_request(struct request *rq)
 {
 	__blk_mq_requeue_request(rq);
-	blk_clear_rq_complete(rq);
 
 	BUG_ON(blk_queued_rq(rq));
 	blk_mq_add_to_requeue_list(rq, true);
-- 
1.7.9.5

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