linux-kernel - Re: bug in tag handling in blk-mq?

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Message-ID: <1525885030.15732.6.camel@gmx.de>
Date:   Wed, 09 May 2018 18:57:10 +0200
From:   Mike Galbraith <efault@....de>
To:     Jens Axboe <axboe@...nel.dk>,
        Paolo Valente <paolo.valente@...aro.org>
Cc:     Christoph Hellwig <hch@....de>,
        linux-block <linux-block@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>
Subject: Re: bug in tag handling in blk-mq?

On Wed, 2018-05-09 at 09:18 -0600, Jens Axboe wrote:
> On 5/8/18 10:11 PM, Mike Galbraith wrote:
> > On Tue, 2018-05-08 at 19:09 -0600, Jens Axboe wrote:
> >>
> >> Alright, I managed to reproduce it. What I think is happening is that
> >> BFQ is limiting the inflight case to something less than the wake
> >> batch for sbitmap, which can lead to stalls. I don't have time to test
> >> this tonight, but perhaps you can give it a go when you are back at it.
> >> If not, I'll try tomorrow morning.
> >>
> >> If this is the issue, I can turn it into a real patch. This is just to
> >> confirm that the issue goes away with the below.
> > 
> > Confirmed.  Impressive high speed bug stomping.
> 
> Well, that's good news. Can I get you to try this patch?

Sure thing.  The original hang (minus provocation patch) being
annoyingly non-deterministic, this will (hopefully) take a while.

	-Mike