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From: Daniel Harding <[email protected]>
To: Pavel Begunkov <[email protected]>, Jens Axboe <[email protected]>
Cc: [email protected], [email protected],
	[email protected]
Subject: Re: [REGRESSION] lxc-stop hang on 5.17.x kernels
Date: Mon, 2 May 2022 21:49:40 +0300	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 5/2/22 20:40, Pavel Begunkov wrote:
> On 5/2/22 18:00, Jens Axboe wrote:
>> On 5/2/22 7:59 AM, Jens Axboe wrote:
>>> 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.
>>
>> Didn't manage to reproduce. Can you try, on both the good and bad
>> kernel, to do:
>
> Same here, it doesn't reproduce for me
OK, sorry it wasn't something simple.
> # echo 1 > /sys/kernel/debug/tracing/events/io_uring/enable
>>
>> run lxc-stop
>>
>> # cp /sys/kernel/debug/tracing/trace ~/iou-trace
>>
>> so we can see what's going on? Looking at the source, lxc is just using
>> plain POLL_ADD, so I'm guessing it's not getting a notification when it
>> expects to, or it's POLL_REMOVE not doing its job. If we have a trace
>> from both a working and broken kernel, that might shed some light on it.
It's late in my timezone, but I'll try to work on getting those traces 
tomorrow.

-- 
Regards,

Daniel Harding

  reply	other threads:[~2022-05-02 18:49 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-02 13:17 [REGRESSION] lxc-stop hang on 5.17.x kernels Daniel Harding
2022-05-02 13:26 ` Jens Axboe
2022-05-02 13:36   ` Daniel Harding
2022-05-02 13:59     ` Jens Axboe
2022-05-02 17:00       ` Jens Axboe
2022-05-02 17:40         ` Pavel Begunkov
2022-05-02 18:49           ` Daniel Harding [this message]
2022-05-02 23:14             ` Pavel Begunkov
2022-05-03  7:37               ` Daniel Harding
2022-05-03 14:14                 ` Pavel Begunkov
2022-05-04  6:54                   ` Daniel Harding
2022-05-15  8:20                     ` Thorsten Leemhuis
2022-05-15 18:34                       ` Daniel Harding
2022-05-16 12:12                         ` Pavel Begunkov
2022-05-16 13:25                           ` Pavel Begunkov
2022-05-16 13:57                             ` Daniel Harding
2022-05-16 15:13                               ` Daniel Harding
2022-05-16 18:13                                 ` Pavel Begunkov
2022-05-17  8:19                                   ` Christian Brauner
2022-05-17 10:31                                     ` Pavel Begunkov
2022-05-16 18:17                                 ` Thorsten Leemhuis
2022-05-16 18:22                                   ` Jens Axboe
2022-05-16 18:34                                     ` Thorsten Leemhuis
2022-05-16 18:39                                       ` Jens Axboe
2022-05-16 19:07                                         ` Thorsten Leemhuis
2022-05-16 19:14                                           ` Jens Axboe

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