linux-kernel - Re: [REGRESSION] lxc-stop hang on 5.17.x kernels

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Date:   Mon, 2 May 2022 07:59:47 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Daniel Harding <dharding@...ing180.net>,
        Pavel Begunkov <asml.silence@...il.com>
Cc:     regressions@...ts.linux.dev, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [REGRESSION] lxc-stop hang on 5.17.x kernels

On 5/2/22 7:36 AM, Daniel Harding wrote:
> On 5/2/22 16:26, Jens Axboe wrote:
>> On 5/2/22 7:17 AM, Daniel Harding wrote:
>>> I use lxc-4.0.12 on Gentoo, built with io-uring support
>>> (--enable-liburing), targeting liburing-2.1.  My kernel config is a
>>> very lightly modified version of Fedora's generic kernel config. After
>>> moving from the 5.16.x series to the 5.17.x kernel series, I started
>>> noticed frequent hangs in lxc-stop.  It doesn't happen 100% of the
>>> time, but definitely more than 50% of the time.  Bisecting narrowed
>>> down the issue to commit aa43477b040251f451db0d844073ac00a8ab66ee:
>>> io_uring: poll rework. Testing indicates the problem is still present
>>> in 5.18-rc5. Unfortunately I do not have the expertise with the
>>> codebases of either lxc or io-uring to try to debug the problem
>>> further on my own, but I can easily apply patches to any of the
>>> involved components (lxc, liburing, kernel) and rebuild for testing or
>>> validation.  I am also happy to provide any further information that
>>> would be helpful with reproducing or debugging the problem.
>> Do you have a recipe to reproduce the hang? That would make it
>> significantly easier to figure out.
> 
> I can reproduce it with just the following:
> 
>     sudo lxc-create --n lxc-test --template download --bdev dir --dir /var/lib/lxc/lxc-test/rootfs -- -d ubuntu -r bionic -a amd64
>     sudo lxc-start -n lxc-test
>     sudo lxc-stop -n lxc-test
> 
> The lxc-stop command never exits and the container continues running.
> If that isn't sufficient to reproduce, please let me know.

Thanks, that's useful! I'm at a conference this week and hence have
limited amount of time to debug, hopefully Pavel has time to take a look
at this.

-- 
Jens Axboe