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Date:   Wed, 5 Jul 2023 10:51:57 +0200
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Subject: Re: Fwd: Memory corruption in multithreaded user space program while
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To:     Suren Baghdasaryan <surenb@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Linux regressions mailing list <regressions@lists.linux.dev>,
        Bagas Sanjaya <bagasdotme@gmail.com>,
        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>,
        Greg KH <gregkh@linuxfoundation.org>
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From:   "Linux regression tracking (Thorsten Leemhuis)" 
        <regressions@leemhuis.info>
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In-Reply-To: <2023070509-undertow-pulverize-5adc@gregkh>
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On 05.07.23 09:08, Greg KH wrote:
> On Tue, Jul 04, 2023 at 01:22:54PM -0700, Suren Baghdasaryan wrote:
>> On Tue, Jul 4, 2023 at 9:18 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>>> On Tue, 4 Jul 2023 09:00:19 +0100 Greg KH <gregkh@linuxfoundation.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.

Andrew, how long will you remain in "wait-a-few-days-mode"? Given what
Greg said below and that we already had three reports I know of I'd
prefer if we could fix this rather sooner than later in mainline --
especially as Arch Linux and openSUSE Tumbleweed likely have switched to
6.4.y already or will do so soon.

>> 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@vger?
> 
> We can't do anything for stable until it lands in Linus's tree, so if
> you didn't happen to have the stable@ tag in the patch, just email us
> the git SHA1 and I can pick it up that way.
> 
> thanks,
> 
> greg k-h

Ciao, Thorsten