linux-kernel - Re: [PATCH] scsi-mq: fix hw queue hang caused by timeout

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Message-ID: <541C3BD8.2070206@fb.com>
Date:	Fri, 19 Sep 2014 08:21:12 -0600
From:	Jens Axboe <axboe@...com>
To:	Ming Lei <ming.lei@...onical.com>
CC:	Christoph Hellwig <hch@....de>,
	James Bottomley <JBottomley@...allels.com>,
	Linux SCSI List <linux-scsi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Douglas Gilbert <dgilbert@...erlog.com>
Subject: Re: [PATCH] scsi-mq: fix hw queue hang caused by timeout

On 09/19/2014 08:18 AM, Ming Lei wrote:
> On Fri, Sep 19, 2014 at 9:07 PM, Ming Lei <ming.lei@...onical.com> wrote:
>> On Fri, Sep 19, 2014 at 1:03 AM, Jens Axboe <axboe@...com> wrote:
>>> On 2014-09-18 10:35, Christoph Hellwig wrote:
>>>>
>>>> On Thu, Sep 18, 2014 at 11:59:10PM +0800, Ming Lei wrote:
>>>>>
>>>>> If there are two requests or more timed out, the dispatch queue
>>>>> is put into stopped state and never be recoverd, and there
>>>>> is no such problem in non-mq mode.
>>>>>
>>>>> This patch trys to recover the stopped queue when the queue
>>>>> becomes unbusy, then the following retries can move on.
>>>>>
>>>>> Basically this patch maintains same behavior for this situation
>>>>> with non-mq mode.
>>>>
>>>>
>>>> This looks somewhat similar to the issues that Doug reported, and I
>>>> remember
>>>> when he was last running into boot problems it was timeout related, too.
>>>>
>>>> As far as the implementation is concerned I think the correct fix is
>>>> to clear the BLK_MQ_S_STOPPED queue flags in blk_mq_kick_requeue_list.
>>>
>>>
>>> Since that's the kick part of the requeue, auto-starting the queue for that
>>> makes a lot of sense. I say that's the way we go.
>>
>> Yeah, that looks better.
>>
>> But it doesn't work after the simple change, and I need to
>> investigate further.
> 
> It is because of the timer miss, now it starts to work.

Excellent. I think most new issues should be fixed in for-linus for
inclusion in this round. It's much bigger than I hoped for this late in
the cycle, but lots of us have run a lot of testing, so that's not a
huge worry.

-- 
Jens Axboe

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