linux-kernel - Re: [PATCH 06/14] block: store elevator state in request

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Message-ID: <8654edbf-0161-5dc1-5133-2d0623628229@kernel.dk>
Date:   Tue, 19 Oct 2021 16:26:06 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Guillaume Tucker <guillaume.tucker@...labora.com>
Cc:     linux-block@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernelci@...ups.io" <kernelci@...ups.io>
Subject: Re: [PATCH 06/14] block: store elevator state in request

On 10/19/21 4:21 PM, Guillaume Tucker wrote:
> Hi Jens,
> 
> On 17/10/2021 02:37, Jens Axboe wrote:
>> Add an rq private RQF_ELV flag, which tells the block layer that this
>> request was initialized on a queue that has an IO scheduler attached.
>> This allows for faster checking in the fast path, rather than having to
>> deference rq->q later on.
>>
>> Elevator switching does full quiesce of the queue before detaching an
>> IO scheduler, so it's safe to cache this in the request itself.
> 
> A kernelci.org automated bisection found that this patch
> introduced a regression in next-20211019 with a NULL pointer
> dereference, which only seems to be affecting QEMU but across all
> architectures.
> 
> More details about the regression can be found here:
> 
>   https://linux.kernelci.org/test/job/next/branch/master/kernel/next-20211019/plan/baseline/
>   https://linux.kernelci.org/test/case/id/616ea20eb7104071c43358ea/
> 
> See also all the test jobs involved in the automated bisection:
> 
>   https://lava.collabora.co.uk/scheduler/device_type/qemu?dt_search=bisection-287
> 
> If you do send a fix, please include this trailer:
> 
>   Reported-by: "kernelci.org bot" <bot@...nelci.org>
> 
> 
> Please let us know if this seems like a valid bisection result
> and if you need any help to debug the issue or try a fix.

This got fixed yesterday, current tree is fine.

-- 
Jens Axboe