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Message-ID: <ccf6cea1-1139-cd73-c4e5-dc9799708bdd@living180.net>
Date:   Mon, 2 May 2022 16:36:25 +0300
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Subject: Re: [REGRESSION] lxc-stop hang on 5.17.x kernels
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To:     Jens Axboe <axboe@kernel.dk>,
        Pavel Begunkov <asml.silence@gmail.com>
Cc:     regressions@lists.linux.dev, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <7925e262-e0d4-6791-e43b-d37e9d693414@living180.net>
 <6ad38ecc-b2a9-f0e9-f7c7-f312a2763f97@kernel.dk>
From:   Daniel Harding <dharding@living180.net>
In-Reply-To: <6ad38ecc-b2a9-f0e9-f7c7-f312a2763f97@kernel.dk>
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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.

-- 
Regards,

Daniel Harding