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SubjectRe: [PATCH BUGFIX 1/1] block, bfq: add requeue-request hook
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> Il giorno 07 feb 2018, alle ore 11:27, Paolo Valente <paolo.valente@linaro.org> ha scritto:
>
>
>
>> Il giorno 07 feb 2018, alle ore 11:15, Mike Galbraith <efault@gmx.de> ha scritto:
>>
>> On Wed, 2018-02-07 at 10:45 +0100, Paolo Valente wrote:
>>>
>>>> Il giorno 07 feb 2018, alle ore 10:23, Mike Galbraith <efault@gmx.de> ha scritto:
>>>>
>>>> On Wed, 2018-02-07 at 10:08 +0100, Paolo Valente wrote:
>>>>>
>>>>> The first piece of information I need is whether this failure happens
>>>>> even without "BFQ hierarchical scheduling support".
>>>>
>>>> I presume you mean BFQ_GROUP_IOSCHED, which I do not have enabled.
>>>>
>>>
>>> Great (so to speak), this saves us one step.
>>>
>>> So, here's my next request for help: please apply the attached patch
>>> (compressed to preserve it from my email client) and retry. It adds
>>> several anomaly checks. I hope I have not added any false-positive
>>> check.
>>
>> kernel BUG at block/bfq-iosched.c:4742!
>>
>> 4742 BUG_ON(!(rq->rq_flags & RQF_ELVPRIV));
>
> Oh my, this is as crazy as, fortunately, easy to fix. The problem is
> that this is easy to fix in bfq, but increases the doubts I have
> expressed in my cover letter: is it ok that, in blk-mq, the functions
> of an elevator may get invoked, without control, on requests that do
> not belong to that elevator?
>
> Anyway, two requests, Mike, if you haven't had enough already:
>
> 1. Could you paste a stack trace for this OOPS, just to understand how we
> get there?
>
> 2. Could you please turn that BUG_ON into:
> if (!(rq->rq_flags & RQF_ELVPRIV))
> return;
> and see what happens?
>

Hi Oleksandr, Holger,
before I prepare a V2 candidate patch, could you please test my
instrumentation patch too, with the above change made. For your
convenience, I have attached a compressed archive with both the
instrumentation patch and a patch making the above change.

Crossing my fingers,
Paolo




> Thanks a lot,
> Paolo

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