* [PATCH V2] blk-mq: don't grab rq's refcount in blk_mq_check_expired()
@ 2021-08-11 15:52 Ming Lei
2021-08-12 8:55 ` Christoph Hellwig
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: Ming Lei @ 2021-08-11 15:52 UTC (permalink / raw)
To: Jens Axboe
Cc: linux-block, Christoph Hellwig, Bart Van Assche, John Garry,
Ming Lei, Keith Busch
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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH V2] blk-mq: don't grab rq's refcount in blk_mq_check_expired()
2021-08-11 15:52 [PATCH V2] blk-mq: don't grab rq's refcount in blk_mq_check_expired() Ming Lei
@ 2021-08-12 8:55 ` Christoph Hellwig
2021-08-12 9:40 ` John Garry
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Christoph Hellwig @ 2021-08-12 8:55 UTC (permalink / raw)
To: Ming Lei
Cc: Jens Axboe, linux-block, Christoph Hellwig, Bart Van Assche,
John Garry, Keith Busch
Looks good,
Reviewed-by: Christoph Hellwig <hch@lst.de>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH V2] blk-mq: don't grab rq's refcount in blk_mq_check_expired()
2021-08-11 15:52 [PATCH V2] blk-mq: don't grab rq's refcount in blk_mq_check_expired() Ming Lei
2021-08-12 8:55 ` Christoph Hellwig
@ 2021-08-12 9:40 ` John Garry
2021-08-17 1:03 ` Ming Lei
2021-08-17 14:33 ` Jens Axboe
3 siblings, 0 replies; 5+ messages in thread
From: John Garry @ 2021-08-12 9:40 UTC (permalink / raw)
To: Ming Lei, Jens Axboe
Cc: linux-block, Christoph Hellwig, Bart Van Assche, Keith Busch
On 11/08/2021 16:52, Ming Lei wrote:
> 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>
Reviewed-by: John Garry <john.garry@huawei.com>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH V2] blk-mq: don't grab rq's refcount in blk_mq_check_expired()
2021-08-11 15:52 [PATCH V2] blk-mq: don't grab rq's refcount in blk_mq_check_expired() Ming Lei
2021-08-12 8:55 ` Christoph Hellwig
2021-08-12 9:40 ` John Garry
@ 2021-08-17 1:03 ` Ming Lei
2021-08-17 14:33 ` Jens Axboe
3 siblings, 0 replies; 5+ messages in thread
From: Ming Lei @ 2021-08-17 1:03 UTC (permalink / raw)
To: Jens Axboe
Cc: linux-block, Christoph Hellwig, Bart Van Assche, John Garry, Keith Busch
On Wed, Aug 11, 2021 at 11:52:02PM +0800, Ming Lei wrote:
> 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
>
Hello Jens,
Ping...
Thanks,
Ming
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH V2] blk-mq: don't grab rq's refcount in blk_mq_check_expired()
2021-08-11 15:52 [PATCH V2] blk-mq: don't grab rq's refcount in blk_mq_check_expired() Ming Lei
` (2 preceding siblings ...)
2021-08-17 1:03 ` Ming Lei
@ 2021-08-17 14:33 ` Jens Axboe
3 siblings, 0 replies; 5+ messages in thread
From: Jens Axboe @ 2021-08-17 14:33 UTC (permalink / raw)
To: Ming Lei
Cc: linux-block, Christoph Hellwig, Bart Van Assche, John Garry, Keith Busch
On 8/11/21 9:52 AM, Ming Lei wrote:
> 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().
Applied, thanks Ming.
--
Jens Axboe
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-08-17 14:35 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-08-11 15:52 [PATCH V2] blk-mq: don't grab rq's refcount in blk_mq_check_expired() Ming Lei
2021-08-12 8:55 ` 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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