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Date:   Tue, 4 Jul 2023 09:00:19 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     Linux regressions mailing list <regressions@lists.linux.dev>,
        Bagas Sanjaya <bagasdotme@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jacob Young <jacobly.alt@gmail.com>,
        Laurent Dufour <ldufour@linux.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Memory Management <linux-mm@kvack.org>,
        Linux PowerPC <linuxppc-dev@lists.ozlabs.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: Fwd: Memory corruption in multithreaded user space program while
 calling fork
Message-ID: <2023070453-plod-swipe-cfbf@gregkh>
References: <facbfec3-837a-51ed-85fa-31021c17d6ef@gmail.com>
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 <CAJuCfpH7BOBYGEG=op09bZrh1x3WA8HMcGBXXRhe6M5RJaen5A@mail.gmail.com>
 <CAJuCfpH7t7gCV2FkctzG2eWTUVTFZD7CtD14-WuHqBqOYBo1jA@mail.gmail.com>
 <2023070359-evasive-regroup-f3b8@gregkh>
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On Tue, Jul 04, 2023 at 12:45:39AM -0700, Suren Baghdasaryan wrote:
> On Mon, Jul 3, 2023 at 11:44 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Mon, Jul 03, 2023 at 11:27:19AM -0700, Suren Baghdasaryan wrote:
> > > On Mon, Jul 3, 2023 at 11:08 AM Suren Baghdasaryan <surenb@google.com> wrote:
> > > >
> > > > On Mon, Jul 3, 2023 at 2:53 AM Linux regression tracking (Thorsten
> > > > Leemhuis) <regressions@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.
> > >
> > > Posted at: https://lore.kernel.org/all/20230703182150.2193578-1-surenb@google.com/
> >
> > As that change fixes something in 6.4, why not cc: stable on it as well?
> 
> Sorry, I thought since per-VMA locks were introduced in 6.4 and this
> patch is fixing 6.4 I didn't need to send it to stable for older
> versions. Did I miss something?

6.4.y is a stable kernel tree right now, so yes, it needs to be included
there :)