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

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Message-ID: <20140918163549.GB3950@lst.de>
Date:	Thu, 18 Sep 2014 18:35:49 +0200
From:	Christoph Hellwig <hch@....de>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	James Bottomley <JBottomley@...allels.com>,
	Jens Axboe <axboe@...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 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.
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