linux-kernel - Re: Fwd: Memory corruption in multithreaded user space program while calling fork

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Date:   Mon, 3 Jul 2023 11:53:05 +0200
From:   "Linux regression tracking (Thorsten Leemhuis)" 
        <regressions@...mhuis.info>
To:     Bagas Sanjaya <bagasdotme@...il.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jacob Young <jacobly.alt@...il.com>,
        Laurent Dufour <ldufour@...ux.ibm.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Regressions <regressions@...ts.linux.dev>,
        Linux Memory Management <linux-mm@...ck.org>,
        Linux PowerPC <linuxppc-dev@...ts.ozlabs.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: Fwd: Memory corruption in multithreaded user space program while
 calling fork

On 02.07.23 14:27, Bagas Sanjaya wrote:
> I notice a regression report on Bugzilla [1]. Quoting from it:
> 
>> After upgrading to kernel version 6.4.0 from 6.3.9, I noticed frequent but random crashes in a user space program.  After a lot of reduction, I have come up with the following reproducer program:
> [...]
>> After tuning the various parameters for my computer, exit code 2, which indicates that memory corruption was detected, occurs approximately 99% of the time.  Exit code 1, which occurs approximately 1% of the time, means it ran out of statically-allocated memory before reproducing the issue, and increasing the memory usage any more only leads to diminishing returns.  There is also something like a 0.1% chance that it segfaults due to memory corruption elsewhere than in the statically-allocated buffer.
>>
>> With this reproducer in hand, I was able to perform the following bisection:
> [...]
>
> See Bugzilla for the full thread.

Additional details from
https://bugzilla.kernel.org/show_bug.cgi?id=217624#c5 :

```
I can confirm that v6.4 with 0bff0aaea03e2a3ed6bfa302155cca8a432a1829
reverted no longer causes any memory corruption with either my
reproducer or the original program.
```

FWIW: 0bff0aaea03 ("x86/mm: try VMA lock-based page fault handling
first") [merged for v6.4-rc1, authored by Suren Baghdasaryan [already CCed]]

That's the same commit that causes build problems with go:

https://lore.kernel.org/all/dbdef34c-3a07-5951-e1ae-e9c6e3cdf51b@kernel.org/

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
Everything you wanna know about Linux kernel regression tracking:
https://linux-regtracking.leemhuis.info/about/#tldr
If I did something stupid, please tell me, as explained on that page.

#regzbot introduced: 0bff0aaea03e2a3