From: Ming Lei <ming.lei@redhat.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
Bart Van Assche <bvanassche@acm.org>,
John Garry <john.garry@huawei.com>,
Ming Lei <ming.lei@redhat.com>, Keith Busch <kbusch@kernel.org>
Subject: [PATCH V2] blk-mq: don't grab rq's refcount in blk_mq_check_expired()
Date: Wed, 11 Aug 2021 23:52:02 +0800 [thread overview]
Message-ID: <20210811155202.629575-1-ming.lei@redhat.com> (raw)
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@kernel.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
V2:
- remove extra request expire check as suggested by Keith
- modify comment a bit
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 d2725f94491d..b5237211ccb7 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -923,34 +923,14 @@ 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;
}
--
2.31.1
next reply other threads:[~2021-08-11 15:52 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-11 15:52 Ming Lei [this message]
2021-08-12 8:55 ` [PATCH V2] blk-mq: don't grab rq's refcount in blk_mq_check_expired() Christoph Hellwig
2021-08-12 9:40 ` John Garry
2021-08-17 1:03 ` Ming Lei
2021-08-17 14:33 ` Jens Axboe
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