linux-kernel - Re: [PATCH v4 2/6] nbd: convert to use blk_mq_find_and_get

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Message-ID: <YThtq154oyROxBj9@T590>
Date:   Wed, 8 Sep 2021 16:00:43 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     "yukuai (C)" <yukuai3@...wei.com>
Cc:     axboe@...nel.dk, josef@...icpanda.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, nbd@...er.debian.org,
        yi.zhang@...wei.com
Subject: Re: [PATCH v4 2/6] nbd: convert to use blk_mq_find_and_get_req()

On Wed, Sep 08, 2021 at 03:37:06PM +0800, yukuai (C) wrote:
> On 2021/09/08 15:30, Ming Lei wrote:
> 
> > > +put_req:
> > > +	if (req)
> > > +		blk_mq_put_rq_ref(req);
> > >   	return ret ? ERR_PTR(ret) : cmd;
> > 
> > After the request's refcnt is dropped, it can be freed immediately, then
> > one stale command is returned to caller.
> 
> Hi, Ming
> 
> It's right this patch leave this problem. Please take a look at patch 3
> and patch 4, the problem should be fixed with these patches.

Not see it is addressed in patch 3 & 4, and it is one obvious fault in
patch 2, please fix it from beginning by moving the refcnt drop
into recv_work().

BTW, the approach in patch 3 looks fine, which is very similar with
SCSI's handling.

Thanks,
Ming