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From: Jens Axboe <[email protected]>
To: Thorsten Leemhuis <[email protected]>,
	Daniel Harding <[email protected]>,
	Pavel Begunkov <[email protected]>
Cc: [email protected], [email protected],
	[email protected],
	Christian Brauner <[email protected]>
Subject: Re: [REGRESSION] lxc-stop hang on 5.17.x kernels
Date: Mon, 16 May 2022 13:14:20 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 5/16/22 1:07 PM, Thorsten Leemhuis wrote:
> 
> 
> On 16.05.22 20:39, Jens Axboe wrote:
>> On 5/16/22 12:34 PM, Thorsten Leemhuis wrote:
>>> On 16.05.22 20:22, Jens Axboe wrote:
>>>> On 5/16/22 12:17 PM, Thorsten Leemhuis wrote:
>>>>>>> Pavel, I had actually just started a draft email with the same theory
>>>>>>> (although you stated it much more clearly than I could have).  I'm
>>>>>>> working on debugging the LXC side, but I'm pretty sure the issue is
>>>>>>> due to LXC using blocking reads and getting stuck exactly as you
>>>>>>> describe.  If I can confirm this, I'll go ahead and mark this
>>>>>>> regression as invalid and file an issue with LXC. Thanks for your help
>>>>>>> and patience.
>>>>>>
>>>>>> Yes, it does appear that was the problem.  The attach POC patch against
>>>>>> LXC fixes the hang.  The kernel is working as intended.
>>>>>>
>>>>>> #regzbot invalid:  userspace programming error
>>>>>
>>>>> Hmmm, not sure if I like this. So yes, this might be a bug in LXC, but
>>>>> afaics it's a bug that was exposed by kernel change in 5.17 (correct me
>>>>> if I'm wrong!). The problem thus still qualifies as a kernel regression
>>>>> that normally needs to be fixed, as can be seen my some of the quotes
>>>>> from Linus in this file:
>>>>> https://www.kernel.org/doc/html/latest/process/handling-regressions.html
>>>>
>>>> Sorry, but that's really BS in this particularly case. This could always
>>>> have triggered, it's the way multishot works. Will we count eg timing
>>>> changes as potential regressions, because an application relied on
>>>> something there? That does not make it ABI.
>>>>
>>>> In general I agree with Linus on this, a change in behavior breaking
>>>> something should be investigated and figured out (and reverted, if need
>>>> be). This is not that.
>>>
>>> Sorry, I have to deal with various subsystems and a lot of regressions
>>> reports. I can't know the details of each of issue and there are
>>> developers around that are not that familiar with all the practical
>>> implications of the "no regressions". That's why I was just trying to
>>> ensure that this is something safe to ignore. If you say it is, than I'm
>>> totally happy and now rest my case. :-D
>>
>> It's just a slippery slope that quickly leads to the fact that _any_
>> kernel change is a potential regressions,
> 
> I know, don't worry, that's why I'm trying to be careful. But I also had
> cases already where someone (even a proper subsystem maintainer) said
> "this is not a regression, it's a userspace bug" and it clearly was a
> kernel regression (and Linus wasn't happy when he found out). That why I

I get where you're coming from, and that is indeed what most maintainers
would say :-)

-- 
Jens Axboe


      reply	other threads:[~2022-05-16 19:14 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
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 [this message]

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