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Date:	Fri, 19 Sep 2014 22:18:48 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Jens Axboe <axboe@...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 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.

Thanks,
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