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

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Message-ID: <541B105E.1030507@fb.com>
Date:	Thu, 18 Sep 2014 11:03:26 -0600
From:	Jens Axboe <axboe@...com>
To:	Christoph Hellwig <hch@....de>, Ming Lei <ming.lei@...onical.com>
CC:	James Bottomley <JBottomley@...allels.com>,
	<linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Douglas Gilbert <dgilbert@...erlog.com>
Subject: Re: [PATCH] scsi-mq: fix hw queue hang caused by timeout

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.

-- 
Jens Axboe

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