linux-kernel - Re: blk_mq_sched_insert_request: inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage

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Message-ID: <87lgn9dqx3.fsf@concordia.ellerman.id.au>
Date:   Fri, 28 Jul 2017 16:19:36 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Jens Axboe <axboe@...nel.dk>,
        Bart Van Assche <Bart.VanAssche@....com>,
        Brian J King <bjking1@...ibm.com>
Cc:     "linuxppc-dev\@lists.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block\@vger.kernel.org" <linux-block@...r.kernel.org>
Subject: Re: blk_mq_sched_insert_request: inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage

Jens Axboe <axboe@...nel.dk> writes:
> On 07/27/2017 08:47 AM, Bart Van Assche wrote:
>> On Thu, 2017-07-27 at 08:02 -0600, Jens Axboe wrote:
>>> The bug looks like SCSI running the queue inline from IRQ
>>> context, that's not a good idea.
...
>> 
>> scsi_run_queue() works fine if no scheduler is configured. Additionally, that
>> code predates the introduction of blk-mq I/O schedulers. I think it is
>> nontrivial for block driver authors to figure out that a queue has to be run
>> from process context if a scheduler has been configured that does not support
>> to be run from interrupt context.
>
> No it doesn't, you could never run the queue from interrupt context with
> async == false. So I don't think that's confusing at all, you should
> always be aware of the context.
>
>> How about adding WARN_ON_ONCE(in_interrupt()) to
>> blk_mq_start_hw_queue() or replacing the above patch by the following:
>
> No, I hate having dependencies like that, because they always just catch
> one of them. Looks like the IPR path that hits this should just offload
> to a workqueue or similar, you don't have to make any scsi_run_queue()
> async.

OK, so the resolution is "fix it in IPR" ?

cheers