Re: [PATCH v2] mm/khugepaged: Don't install PMDs in uffd-minor-registered VMAs

[Andrew Morton]

On Fri, 28 Aug 2026 18:09:39 -0700 James Houghton <jthoughton@xxxxxxxxxx> wrote:

> [lots of good stuff]
>

OK, thanks.

> >
> > > Suggested-by: Lance Yang <lance.yang@xxxxxxxxx>
> > > Tested-by: Lance Yang <lance.yang@xxxxxxxxx>
> >
> > Wondering what Lance tested.  Was he able to reproduce the bug?
> 
> I assume he just re-ran my repro, but yeah I'm not sure, heh. Lance,
> what did you test?

Wait, there was a reproducer?

Oh yeah, found it.  You changed the patch Subject: between versions,
dangnabbit.

I asked Gemini to write me a reproducer and it basically said "sorry
andrew, I can't do that".  ChatGPT was much more accommodating but
after a few iterations it was still pretty mind-bending.  I came away
thinking "nobody has ever hit this".

But that's not the point.  Now that it's out there and known about,
Black Hats might be working away to find and utilize a reproducer, so
yes, we backport it.

> > Sashiko might have found another race in there:
> >
> >         https://sashiko.dev/#/patchset/20260828222640.1638457-1-jthoughton@xxxxxxxxxx
> 
> Let me get back to you on this. Best case, I'll send another
> (separate) patch. :)

Great, another patch ;)