linux-kernel - Re: [PATCH V2 7/8] nvme: use blk_mq_queue_tag_inflight

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Message-ID: <CACVXFVMw9G6n44-knV6oa3FxJ6YzN05ZRajkgUnhLJupnkadOQ@mail.gmail.com>
Date:   Tue, 26 Mar 2019 10:41:00 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     "jianchao.wang" <jianchao.w.wang@...cle.com>
Cc:     Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Keith Busch <keith.busch@...el.com>,
        James Smart <jsmart2021@...il.com>,
        Bart Van Assche <bvanassche@....org>,
        Josef Bacik <josef@...icpanda.com>,
        linux-nvme <linux-nvme@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        Hannes Reinecke <hare@...e.de>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>
Subject: Re: [PATCH V2 7/8] nvme: use blk_mq_queue_tag_inflight_iter

On Tue, Mar 26, 2019 at 9:18 AM jianchao.wang
<jianchao.w.wang@...cle.com> wrote:
>
> Hi Keith
>
> On 3/25/19 9:49 PM, Keith Busch wrote:
> > On Mon, Mar 25, 2019 at 01:38:37PM +0800, Jianchao Wang wrote:
> >> blk_mq_tagset_inflight_iter is not safe that it could get stale request
> >> in tags->rqs[]. Use blk_mq_queue_tag_inflight_iter here. A new helper
> >> interface nvme_iterate_inflight_rqs is introduced to iterate
> >> all of the ns under a ctrl.
> >
> > Nak, NVMe only iterates tags when new requests can't enter, allocated
> > requests can't dispatch, and dispatched commands can't complete. So
> > it is perfectly safe to iterate if the driver takes reasonable steps
> > beforehand.
>
> nvme_dev_disable just quiesce and freeze the request_queue, but not drain the enters.
> So there still could be someone escapes the queue freeze checking and tries to allocate
> request.

The rq->state is just IDLE for these allocated request, so there
shouldn't be issue
in NVMe's case.

Thanks,
Ming