linux-kernel - Re: [PATCH 2/2] blk-mq: Fix request handover from timeout path to normal execution

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Date:   Mon, 2 Apr 2018 22:49:43 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "tj@...nel.org" <tj@...nel.org>
CC:     "kernel-team@...com" <kernel-team@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>
Subject: Re: [PATCH 2/2] blk-mq: Fix request handover from timeout path to
 normal execution

On Mon, 2018-04-02 at 15:16 -0700, tj@...nel.org wrote:
> AFAIK,
> there's one non-critical race condition which has always been there.
> We have a larger race window for that case but don't yet know whether
> that's problematic or not.  If that actually is problematic, we can
> figure out a way to solve that but such effort / added complexity
> doesn't seem justified yet.  No?

Hello Tejun,

Some important block drivers systematically return BLK_EH_RESET_TIMER
from their timeout handler, e.g. the virtio-scsi initiator driver. What
will the consequence be for these drivers if a blk_mq_complete_request()
call is ignored? Will the request for which the completion was ignored
get stuck?

Thanks,

Bart.