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From: Ming Lei <tom.leiming@gmail.com>
To: Bart Van Assche <Bart.VanAssche@sandisk.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"hch@infradead.org" <hch@infradead.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"yizhan@redhat.com" <yizhan@redhat.com>,
	"axboe@fb.com" <axboe@fb.com>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH 1/2] blk-mq: don't complete un-started request in timeout handler
Date: Thu, 16 Mar 2017 00:46:35 +0800	[thread overview]
Message-ID: <20170315164631.GA19203@ming.t460p> (raw)
In-Reply-To: <20170315162158.GA18768@ming.t460p>

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

  reply	other threads:[~2017-03-15 16:46 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-09 13:02 [PATCH 0/2] blk-mq: dying queue fix & improvement Ming Lei
2017-03-09 13:02 ` Ming Lei
2017-03-09 13:02 ` [PATCH 1/2] blk-mq: don't complete un-started request in timeout handler Ming Lei
2017-03-15  0:07   ` Bart Van Assche
2017-03-15  0:07     ` Bart Van Assche
2017-03-15 12:18     ` Ming Lei
2017-03-15 12:40       ` Ming Lei
2017-03-15 15:36         ` Bart Van Assche
2017-03-15 15:36           ` Bart Van Assche
2017-03-15 16:22           ` Ming Lei
2017-03-15 16:22             ` Ming Lei
2017-03-15 16:46             ` Ming Lei [this message]
2017-03-15 21:35             ` Bart Van Assche
2017-03-15 21:35               ` Bart Van Assche
2017-03-16  0:07               ` Ming Lei
2017-03-16  0:07                 ` Ming Lei
2017-03-16 21:35                 ` Bart Van Assche
2017-03-16 21:35                   ` Bart Van Assche
2017-03-17  0:07                   ` Ming Lei
2017-03-15 21:34       ` Bart Van Assche
2017-03-15 21:34         ` Bart Van Assche
2017-03-15 23:41         ` Ming Lei
2017-03-15 14:11   ` Yi Zhang
2017-03-16 21:37   ` Bart Van Assche
2017-03-16 21:37     ` Bart Van Assche
2017-03-09 13:02 ` [PATCH 2/2] blk-mq: start to freeze queue just after setting dying Ming Lei
2017-03-09 16:58   ` Bart Van Assche
2017-03-09 16:58     ` Bart Van Assche
2017-03-10  2:16     ` Ming Lei

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