linux-kernel - Re: [PATCH v4 6/7] blk-mq: fix freeze queue race

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Message-ID: <20150929065556.GE14911@lst.de>
Date:	Tue, 29 Sep 2015 08:55:56 +0200
From:	Christoph Hellwig <hch@....de>
To:	Tejun Heo <tj@...nel.org>
Cc:	Akinobu Mita <akinobu.mita@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>, Ming Lei <tom.leiming@...il.com>,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v4 6/7] blk-mq: fix freeze queue race

On Mon, Sep 28, 2015 at 10:48:39AM -0400, Tejun Heo wrote:
> Ah, you're right.  I was thinking that percpu_ref_switch_to_percpu()
> being called after blk_mq_freeze_queue_start() would be buggy and thus
> the above can't be enough but that is safe as long as the calls are
> properly synchronized.  Hmmm... maybe we should add synchronization to
> those operations from percpu_ref side.

I think that would be very useful, as most users of the code will
have similar issues.
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