linux-kernel - Re: stalling IO regression since linux 5.12, through 5.18

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Date:   Wed, 17 Aug 2022 11:52:54 +0200
From:   Holger Hoffstätte <holger@...lied-asynchrony.com>
To:     Chris Murphy <lists@...orremedies.com>,
        Nikolay Borisov <nborisov@...e.com>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Paolo Valente <paolo.valente@...aro.org>
Cc:     Linux-RAID <linux-raid@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Josef Bacik <josef@...icpanda.com>,
        linux-block <linux-block@...r.kernel.org>
Subject: Re: stalling IO regression since linux 5.12, through 5.18

On 2022-08-16 17:34, Chris Murphy wrote:
> 
> On Tue, Aug 16, 2022, at 11:25 AM, Nikolay Borisov wrote:
>> How about changing the scheduler either mq-deadline or noop, just
>> to see if this is also reproducible with a different scheduler. I
>> guess noop would imply the blk cgroup controller is going to be
>> disabled
> 
> I already reported on that: always happens with bfq within an hour or
> less. Doesn't happen with mq-deadline for ~25+ hours. Does happen
> with bfq with the above patches removed. Does happen with
> cgroup.disabled=io set.
> 
> Sounds to me like it's something bfq depends on and is somehow
> becoming perturbed in a way that mq-deadline does not, and has
> changed between 5.11 and 5.12. I have no idea what's under bfq that
> matches this description.

Chris, just a shot in the dark but can you try the patch from

https://lore.kernel.org/linux-block/20220803121504.212071-1-yukuai1@huaweicloud.com/

on top of something more recent than 5.12? Ideally 5.19 where it applies
cleanly.

No guarantees, I just remembered this patch and your problem sounds like
a lost wakeup. Maybe BFQ just drives the sbitmap in a way that triggers the
symptom.

-h