linux-kernel - Re: [PATCH STABLE 5.10] mm/memory: add non-anonymous page check in the copy_present

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Message-ID: <Y1vpvzaU322ENcEc@x1n>
Date:   Fri, 28 Oct 2022 10:39:59 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Yuanzheng Song <songyuanzheng@...wei.com>,
        akpm@...ux-foundation.org, gregkh@...uxfoundation.org,
        david@...hat.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH STABLE 5.10] mm/memory: add non-anonymous page check in
 the copy_present_page()

On Thu, Oct 27, 2022 at 06:32:01PM -0700, Hugh Dickins wrote:
> Sorry for leading everyone astray: my mistake was to suppose that
> its !PageAnon check was simply to avoid the later BUG_ON(!anon_vma):
> whereas David and Peter now agree that it actually corrects the
> semantics for fork() on file pages.

Thanks for raising this from the start, Hugh.  It's definitely worthwhile
to discuss this topic which is not obvious at all at least to me, and merge
even the same patch would be different before/after such a discussion,
since we're clearer on the side effects.

> 
> I lift my hold on Yuanzheng's patch: nobody actually said "Acked-by",
> but I think the discussion and resolution have given better than that.
> (No 3rd thoughts please!)

I've acked directly on v2, note that after this discussion IMHO the comment
of !Anon check can be slightly improved (e.g. add some more information on
why we decided to not copy the page even if anon_vma existed), but I don't
want to be harsh on any stable backports that helps resolving problems
already in correct ways.

Thanks,

-- 
Peter Xu