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Subject: Re: [PATCH BUGFIX V3] block, bfq: add requeue-request hook
From: Mike Galbraith <efault@gmx.de>
To: Paolo Valente <paolo.valente@linaro.org>
Cc: Oleksandr Natalenko <oleksandr@natalenko.name>,
        Jens Axboe <axboe@kernel.dk>, stable <stable@vger.kernel.org>
Date: Wed, 14 Feb 2018 06:58:30 +0100
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On Tue, 2018-02-13 at 15:30 +0100, Mike Galbraith wrote:
> On Tue, 2018-02-13 at 09:15 +0100, Paolo Valente wrote:
> > 
> > 
> > No bfq in the trace, so probably yet another problem stemming from the
> > interaction between bfq and blk-mq.  Hung tasks seem to wait
> > indefinitely for a tag, and the only bfq patch that affects tag
> > distribution is:
> > a52a69ea89dc block, bfq: limit tags for writes and async I/O
> > 
> > So, for the next step (and as you already decided to do), please retry
> > after adding the above commit to your initial pair:
> > patches/block-bfq:-fix-occurrences-of-request-finish-method-s-old-name.patch
> > patches/block-bfq:-add-requeue-request-hook.patch
> 
> I did it a bit differently, revert that commit in master, and skip it
> in 4.15.3 with the otherwise full set first, and saw no hangs testing
> either. �I then added it to the 2 patch series, and was rewarded
> with... no bloody hang. �So it's not as deterministic as it had
> appeared to be, there's a phase-of-moon factor. �Oh. Joy.

Bah. �I'm back on 4.15.3 with the full set, and it's holding up fine
too, so file this report under "elves 'n' gremlins".

	-Mike