On Tue, Jul 4, 2023 at 2:28 PM Andrew Morton [off-list ref] wrote:

On Tue, 4 Jul 2023 13:22:54 -0700 Suren Baghdasaryan [off-list ref] wrote:

quoted

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

quoted

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

quoted

quoted

quoted

quoted

quoted

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)

This one isn't sufficient for .configs which already have
PER_VMA_LOCK=y.  Using `depends on BROKEN' would be better.

quoted

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

We're still awaiting tester input on this?

Yeah, and it seems to be negative... Anyway, I'll post a dependency on BROKEN.

I think a clean new fully-changelogged two-patch series would be the
best way to handle this.  Please ensure that the [0/2] intro clearly
explains what we're proposing here, and why.

Also, "might slightly regress" is a bit weak.  These things are
measurable, no?  Because a better solution would be to fix 6.4.x and
mainline and leave it at that.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel