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Date:   Fri, 8 Mar 2019 11:13:54 -0700
From:   Keith Busch <keith.busch@intel.com>
To:     Bart Van Assche <bvanassche@acm.org>
Cc:     linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
        Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>
Subject: Re: [PATCH 2/5] blk-mq: Export iterating queue requests
Message-ID: <20190308181353.GA5214@localhost.localdomain>
References: <20190308174006.5032-1-keith.busch@intel.com>
 <20190308174006.5032-2-keith.busch@intel.com>
 <1552068527.45180.25.camel@acm.org>
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On Fri, Mar 08, 2019 at 10:08:47AM -0800, Bart Van Assche wrote:
> On Fri, 2019-03-08 at 10:40 -0700, Keith Busch wrote:
> > A driver may need to iterate a particular queue's tagged request rather
> > than the whole tagset.
> 
> Since iterating over requests triggers race conditions with request execution
> please explain what use case(s) you have in mind and what your plan is to handle
> such race conditions.

That race isn't new. You should only iterate when your queues are quieced
to ensure the request sent to a callback is stable.