Re: [PATCH 1/2] blk-mq: don't complete un-started request in timeout handler

From	Ming Lei <tom.leiming@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/2] blk-mq: don't complete un-started request in timeout handler
Date	2017-03-15 17:50 +0100
Message-ID	<tlkhz-1Qf-3@gated-at.bofh.it> (permalink)
References	(2 earlier) <tlgdY-7yR-13@gated-at.bofh.it> <tlgdY-7yR-11@gated-at.bofh.it> <tlgxj-7FO-11@gated-at.bofh.it> <tljYd-1Jv-3@gated-at.bofh.it> <tljYd-1Jv-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Thu, Mar 16, 2017 at 12:22:01AM +0800, Ming Lei wrote:
> On Wed, Mar 15, 2017 at 03:36:31PM +0000, Bart Van Assche wrote:
> 
> OK, this race should only exist in case that the requeue happens after dispatch
> busy, because COMPLETE flag isn't set. And if the requeue is from io completion,
> no such race because COMPLETE flag is set.
> 
> One solution I thought of is to call blk_mark_rq_complete() before requeuing
> when dispatch busy happened, but that looks a bit silly. Another way is to
> set STARTED flag just after .queue_rq returns BLK_MQ_RQ_QUEUE_OK, which looks
> reasonable too. Any comments on the 2nd solution?

Actually it isn't possible to happen because rq->deadline is just set
in blk_mq_start_request() called from .queue_rq, and it won't trigger
timeout handling even STARTED is observed as true in blk_mq_check_expired()
because timeout period is often set as big enough. So it is still safe, isn't it?

But this situation should have been commented.

Thanks,
Ming

Thread

Re: [PATCH 1/2] blk-mq: don't complete un-started request in timeout  handler Ming Lei <tom.leiming@gmail.com> - 2017-03-15 13:30 +0100
  Re: [PATCH 1/2] blk-mq: don't complete un-started request in timeout  handler Ming Lei <tom.leiming@gmail.com> - 2017-03-15 13:50 +0100
    Re: [PATCH 1/2] blk-mq: don't complete un-started request in timeout  handler Ming Lei <tom.leiming@gmail.com> - 2017-03-15 17:30 +0100
      Re: [PATCH 1/2] blk-mq: don't complete un-started request in timeout  handler Ming Lei <tom.leiming@gmail.com> - 2017-03-15 17:50 +0100
      Re: [PATCH 1/2] blk-mq: don't complete un-started request in timeout  handler Ming Lei <tom.leiming@gmail.com> - 2017-03-16 01:10 +0100
        Re: [PATCH 1/2] blk-mq: don't complete un-started request in timeout handler Ming Lei <tom.leiming@gmail.com> - 2017-03-17 01:10 +0100
  Re: [PATCH 1/2] blk-mq: don't complete un-started request in timeout  handler Ming Lei <tom.leiming@gmail.com> - 2017-03-16 00:50 +0100

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