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

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Date:   Fri, 28 Oct 2022 06:26:14 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Hugh Dickins <hughd@...gle.com>, Peter Xu <peterx@...hat.com>
Cc:     Yuanzheng Song <songyuanzheng@...wei.com>,
        akpm@...ux-foundation.org, gregkh@...uxfoundation.org,
        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 28.10.22 03:32, Hugh Dickins wrote:
> Reinstating Cc stable, which I removed just before the discussion settled.

Sorry for not reading the full thread before and considering Peters 
mail; I had to take short cuts :)

> 
> On Thu, 27 Oct 2022, Peter Xu wrote:
>> ...
>>
>> After a re-read and 2nd thought, I think David has a valid point in that we
>> shouldn't have special handling of !anon pages on CoW during fork(),
>> because that seems to be against the fundamental concept of fork().
>>
>> So now I think I agree the !Anon original check does look a bit cleaner,
>> and also make fork() behavior matching with the old/new kernels, irrelevant
>> of the pin mess.
> 
> Thanks Peter.  So Yuanzheng's patch for 5.10 is exactly right.
> 
> 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.
> 
> 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!)

Unless someone tells me why I am obviously wrong

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb