linux-kernel - Re: [PATCH 1/2] blk-mq: fix race between timeout and queue

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Message-ID: <20140917164400.GA18472@lst.de>
Date:	Wed, 17 Sep 2014 18:44:00 +0200
From:	Christoph Hellwig <hch@....de>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] blk-mq: fix race between timeout and queue_rq

On Wed, Sep 17, 2014 at 05:47:57PM +0800, Ming Lei wrote:
> Either the request is from requeue or just being allocated from
> tag pool, its REQ_ATOM_STARTED flag has been cleared already, so
> don't test it in blk_mq_start_request().
> 
> One memory barrier is needed between writing rq->deadline and
> setting REQ_ATOM_STARTED so that timeout can't happen too early
> if timeout handler reads obsolete rq->deadline caused by out
> of order of the two writes.

Looks reasonable to me,

Reviewed-by: Christoph Hellwig <hch@....de>
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