On Tue, Jul 4, 2023 at 9:18 AM Andrew Morton [off-list ref] wrote:

On Tue, 4 Jul 2023 09:00:19 +0100 Greg KH [off-list ref] wrote:

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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/ (local)

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/ (local)).
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?

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