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Date: Tue, 29 Sep 2015 17:50:08 -0400
From: Tejun Heo <tj@kernel.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: Akinobu Mita <akinobu.mita@gmail.com>, LKML <linux-kernel@vger.kernel.org>,
        Ming Lei <tom.leiming@gmail.com>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v4 6/7] blk-mq: fix freeze queue race
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Hello,

On Tue, Sep 29, 2015 at 11:03:46AM -0400, Tejun Heo wrote:
> On Tue, Sep 29, 2015 at 09:01:31AM -0600, Jens Axboe wrote:
> > I think that would be very useful, it seems sort of half-assed if the caller
> > side has to provide serialization for that.
> 
> Yeah, the thing is init/exit are usually caller synchronized but
> percpu_rwsem's kill/reinit are more of mode-switching operations which
> can be performed concurrently during operation so I think the right
> thing to do here is making it synchronize itself.  Will spin a patch.

Patchset posted

 http://lkml.kernel.org/g/1443563240-29306-1-git-send-email-tj@kernel.org

Unfortunately, the required changes on percpu_ref side ended up
somewhat invasive and don't seem fit for -stable backport.  I think
it'd be a good idea to apply Akinobu's patch for now and then revert
it later when the percpu_ref changes hit mainline.

Thanks.

-- 
tejun