Date:   Sun, 9 Oct 2022 08:45:22 +0200
From:   Thorsten Leemhuis <regressions@...mhuis.info>
To:     Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>,
        linux-kernel@...r.kernel.org
Cc:     Marc Miltenberger <marcmiltenberger@...il.com>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>,
        Slade Watkins <srw@...dewatkins.net>
Subject: Re: BUG reproduced: 6.0.0-RC kernels trigger Firefox snap bug with
 6.0.0-rc3 through 6.0.0-rc7

On 08.10.22 18:43, Mirsad Goran Todorovac wrote:
> On 08. 10. 2022. 15:41, Mirsad Goran Todorovac wrote:
>> On 06. 10. 2022. 18:58, Thorsten Leemhuis wrote:
>>> On 06.10.22 18:43, Mirsad Goran Todorovac wrote:
>>>> On 06. 10. 2022. 15:23, Thorsten Leemhuis wrote:
>>>>> On 06.10.22 14:43, Mirsad Todorovac wrote:
>>>>>> On 10/6/22 14:25, Thorsten Leemhuis wrote:
>>>>>>
>>>>>>> One more question:
>>>>>>>
>>>>>>> On 06.10.22 14:00, Thorsten Leemhuis wrote:
>>>>>>> Were those two vanilla kernels? I asked in #snappy on IRC and was
>>>>>>> told
>>>>>>> that "snapd simply expects some ubuntu bit in patched into the
>>>>>>> kernel if
>>>>>>> it detects that it runs on an official ubuntu install...". This
>>>>>>> was also
>>>>>>> suggested "it probably makes sense to file a but in LP to make the
>>>>>>> kernel team aware".
>>>>>> Yes, last time I tried it with git clone from linux_stable on
>>>>>> kernel.org
>>>>>> and
>>>>>> config-6.0.0-060000-generic from the official Ubuntu mainline build
>>>>> You don't want to do that. Better take the config used to build a
>>>>> working kernel (say 5.19.y) and then build 6.0 with it (after running
>>>>> "make olddefconfig"), because it might be a new kernel option (say
>>>>> for a
>>>>> new security technique) that might cause the problem, as explained
>>>>> here:
>>>>> https://docs.kernel.org/admin-guide/reporting-regressions.html
>>>> If I understood well, that would mean building www.kernel.org git
>>>> linux_stable
>>>> source with Ubuntu's config-5.9.13-051903?
>>> I meant "please download Linux 6.0 (ideally through git, that you have
>>> everything to perform a bisection), add the config from a working kernel
>>> (if config-5.9.13-051903 is one, yeah, then take that) as .config and
>>> then run "make olddefconfig" before compiling and installing the kernel
>>> to see if 6.0 fails with that config that was working.
>>
>> Having done this build with mentioned config-5.19.13-051903-config from
>> Ubuntu's mainline build and your recommended make option
>> had produced a kernel that so far did not exhibit the Firefox snap
>> "tab crash/wrong Verneed record version" bug.
>>
>> However, the uptime is 1d 18h50min, so it might be too early to draw
>> a definite general conclusion.
>>
>> Now, the brave conlusion seems to be that the culprit is one of the
>> modules
>> added in config-6.0.0-060000-generic.
>> [...]

A new module might be one possible explanation for such a situations,
but there are others that are more likely.

> I know that it is uncool to reply one's own email,

No, it's not. At least not in the land of the Linux kernel. :-D

> but this is new development:
> 
> After starting a zoom spawned session, the Firefox snap tab crash
> reappeared.
> 
> I will reinstate that if was done with the config-5.19.13-generic and
> "make olddefconfig"
> followed by a "make -j 10 deb-pkg" build.
> 
> Here is the exact log of my actions:
> 
>   678  10/06/2022 06:44:58 PM  vi config-5.19.13-051913-generic
>   679  10/06/2022 06:45:21 PM  time rm -rf linux_stable_build/
>   680  10/06/2022 06:45:31 PM  time cp -rp linux_stable linux_stable_build
>   681  10/06/2022 06:46:39 PM  time diff -ur linux_stable linux_stable_build
>   682  10/06/2022 06:47:38 PM  cp config-5.19.13-051913-generic
> linux_stable_build/.config
>   683  10/06/2022 06:47:46 PM  cd linux_stable_build
>   684  10/06/2022 06:47:51 PM  make olddefconfig
>   685  10/06/2022 06:48:05 PM  time nice make -j10 deb-pkg

Yeah, then it's pretty certain that his is a regression. But it could be
caused by all sorts of things and I have no idea where to start. We thus
really could need a bisection to find the root of the problem. This will
be hard, as this crash only happens infrequently. Thing is: the Ubuntu
developers likely have a strong interest in this particular issue and
due to their knowledge of snap have way better chances to pin-point the
root case quickly. So submitting a bug report to them might be the best
way forward in this situation, even if the kernel is likely at fault here.

Ciao, Thorsten

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