linux-kernel - Re: [PATCH BUGFIX 1/1] block, bfq: add requeue-request hook

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Message-Id: <899B68CC-5955-4418-8BFF-DC55A743A61B@linaro.org>
Date:   Tue, 6 Feb 2018 10:38:03 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Mike Galbraith <efault@....de>
Cc:     Oleksandr Natalenko <oleksandr@...alenko.name>,
        Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        'Paolo Valente' via bfq-iosched 
        <bfq-iosched@...glegroups.com>,
        Alban Browaeys <alban.browaeys@...il.com>, ming.lei@...hat.com,
        ivan@...ios.org, 169364@...denti.unimore.it,
        Serena Ziviani <ziviani.serena@...il.com>
Subject: Re: [PATCH BUGFIX 1/1] block, bfq: add requeue-request hook



> Il giorno 06 feb 2018, alle ore 08:56, Mike Galbraith <efault@....de> ha scritto:
> 
> On Tue, 2018-02-06 at 08:44 +0100, Oleksandr Natalenko wrote:
>> Hi, Paolo.
>> 
>> I can confirm that this patch fixes cfdisk hang for me. I've also tried 
>> to trigger the issue Mike has encountered, but with no luck (maybe, I 
>> wasn't insistent enough, just was doing dd on usb-storage device in the 
>> VM).
> 
> I was doing kbuilds, and it blew up on me twice.  Switching back to cfq
> seemed to confirm it was indeed the patch causing trouble, but that's
> by no means a certainty.
> 

Hi Mike,
as you can imagine, I didn't get any failure in my pre-submission
tests on this patch.  In addition, it is not that easy to link this
patch, which just adds some internal bfq housekeeping in case of a
requeue, with a corruption of external lists for general I/O
management.

In this respect, as Oleksandr comments point out, by switching from
cfq to bfq, you switch between much more than two schedulers.  Anyway,
who knows ...

Maybe this report will ring a bell with some block-layer expert, or,
hopefully, next feedback will help puzzle this out.

Thanks,
Paolo


> 	-Mike