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Date:   Tue, 23 Jul 2019 09:06:18 +0800
From:   Ming Lei <ming.lei@redhat.com>
To:     Bart Van Assche <bvanassche@acm.org>
Cc:     Jens Axboe <axboe@kernel.dk>, Keith Busch <keith.busch@intel.com>,
        Sagi Grimberg <sagi@grimberg.me>,
        linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
        Max Gurtovoy <maxg@mellanox.com>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 2/5] blk-mq: introduce
 blk_mq_tagset_wait_completed_request()
Message-ID: <20190723010616.GC30776@ming.t460p>
References: <20190722053954.25423-1-ming.lei@redhat.com>
 <20190722053954.25423-3-ming.lei@redhat.com>
 <c2722892-9cbf-0747-58a8-91a99b72bc53@acm.org>
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On Mon, Jul 22, 2019 at 08:25:07AM -0700, Bart Van Assche wrote:
> On 7/21/19 10:39 PM, Ming Lei wrote:
> > blk-mq may schedule to call queue's complete function on remote CPU via
> > IPI, but doesn't provide any way to synchronize the request's complete
> > fn.
> > 
> > In some driver's EH(such as NVMe), hardware queue's resource may be freed &
> > re-allocated. If the completed request's complete fn is run finally after the
> > hardware queue's resource is released, kernel crash will be triggered.
> > 
> > Prepare for fixing this kind of issue by introducing
> > blk_mq_tagset_wait_completed_request().
> 
> An explanation is missing of why the block layer is modified to fix this
> instead of the NVMe driver.

The above commit log has explained that there isn't sync mechanism in
blk-mq wrt. request completion, and there might be similar issue in other
future drivers.


Thanks,
Ming