From: ebiederm@xmission.com (Eric W. Biederman)
To: Nikolay Borisov <n.borisov.lkml@gmail.com>
Cc: containers@lists.linux-foundation.org, jack@suse.cz,
        linux-kernel@vger.kernel.org, serge@hallyn.com
References: <20161010164046.GG24081@quack2.suse.cz>
        <1476171382-11911-1-git-send-email-kernel@kyup.com>
        <674564a4-ff05-b4d6-4a98-8cfc2e609325@kyup.com>
        <87twafci52.fsf@xmission.com>
        <e86b3a4f-51d5-ea61-93f3-883fe2dbcf34@gmail.com>
        <100ecab5-6656-9ed6-c0f4-b9c97eae506a@gmail.com>
Date: Fri, 09 Dec 2016 18:38:57 +1300
In-Reply-To: <100ecab5-6656-9ed6-c0f4-b9c97eae506a@gmail.com> (Nikolay
        Borisov's message of "Thu, 8 Dec 2016 10:14:50 +0200")
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Nikolay Borisov <n.borisov.lkml@gmail.com> writes:

> On  8.12.2016 08:58, Nikolay Borisov wrote:
>> 
>> 
>> On  8.12.2016 03:40, Eric W. Biederman wrote:
>>> Nikolay Borisov <kernel@kyup.com> writes:
>>>
>>>> Gentle ping, now that rc1 has shipped and Jan's sysctl concern hopefully
>>>> resolved.
>>>
>>> After getting slowed down by some fixes I am now taking a hard look at
>>> your patch in the hopes of merging it.
>>>
>>> Did you happen to see the kbuild test roboot boot failures and did you
>>> happen to look into what caused them?  I have just skimmed them and it
>>> appears to be related to your patch.
>> 
>> I saw them in the beginning but they did look like a generic memory
>> corruption and I believe at the time those patches were submitted there
>> was a lingering memory corruption hitting various patches. Thus I didn't
>> think it was related to my patches. I've since left my work so been
>> taking a bit of time off and haven't looked really hard, so those
>> patches have been kind of lingering.
>> 
>> 
>> But now that you mention it I will try and take a second look to see
>> what might cause the memory corruption? Is there a way to force 0day to
>> re-run them to see whether the failure was indeed caused by my patches
>> or were intermittent?
>
> Ok, I took another look into the report but bear in mind that the
> corruption indeed happened in retire_userns_sysctls. But also this row
> in the report leads me to believe it's not my patch that's the culprit:
>
> [   65.527277] INFO: Allocated in setup_userns_sysctls+0x3f/0xa6 age=5
> cpu=1 pid=418
> [   65.558397] INFO: Freed in free_ctx+0x1d/0x20 age=6 cpu=0 pid=19
>
>
> So a free_ctx function did free it originally, likely causing the
> corruption. And there is no such function involved in the code I'm touching.

Yes.  I read through your patch carefully and it doesn't look like it
could possibly cause that kind of corruption, the code is just too
simple.

So I have (belatedly) placed this change in linux-next.

Eric