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

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Message-ID: <CAJuCfpE_WjRQoDT1XnvBghCH-kpqk+pfcBJGyDnK7DZLMVG5Mw@mail.gmail.com>
Date:   Tue, 4 Jul 2023 13:22:54 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Linux regressions mailing list <regressions@...ts.linux.dev>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Jacob Young <jacobly.alt@...il.com>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        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 Tue, Jul 4, 2023 at 9:18 AM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Tue, 4 Jul 2023 09:00:19 +0100 Greg KH <gregkh@...uxfoundation.org> wrote:
>
> > > > > > 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 :)
>
> I'm in wait-a-few-days-mode on this.  To see if we have a backportable
> fix rather than disabling the feature in -stable.

Ok, I think we have a fix posted at [2]  and it's cleanly applies to
6.4.y stable branch as well. However fork() performance might slightly
regress, therefore disabling per-VMA locks by default for now seems to
be preferable even with this fix (see discussion at
https://lore.kernel.org/all/54cd9ffb-8f4b-003f-c2d6-3b6b0d2cb7d9@google.com/).
IOW, both [1] and [2] should be applied to 6.4.y stable. Both apply
cleanly and I CC'ed stable on [2]. Greg, should I send [1] separately
to stable@...r?

[1] https://lore.kernel.org/all/20230703182150.2193578-1-surenb@google.com/
[2] https://lore.kernel.org/all/20230704200656.2526715-1-surenb@google.com/

>