Fwd: Memory corruption in multithreaded user space program while calling fork

[Suren Baghdasaryan]

On Mon, Jul 3, 2023 at 2:53 AM Linux regression tracking (Thorsten
Leemhuis) <regressions at leemhuis.info> wrote:
>
> 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/

Thanks! I'll investigate this later today. After discussing with
Andrew, we would like to disable CONFIG_PER_VMA_LOCK by default until
the issue is fixed. I'll post a patch shortly.

>
> Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
> --
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>
> #regzbot introduced: 0bff0aaea03e2a3