Re: [RFC for stable 5.15 and 5.10] mm/memory: only copy anonymous pages during fork()

[David Hildenbrand <david@redhat.com>]

On 13.11.24 17:18, Vlastimil Babka wrote:
> On 11/13/24 17:09, David Hildenbrand wrote:
>>> ---
>>> Hi, we've seen this in our 5.14 based kernel and it involved the out of
>>> tree gpfs module, but I believe the same thing can happen in LTS's 5.10
>>> and 5.15 without out of tree modules as well. So I'd like your opinion
>>> on this fix before I propose it to stable as a non-standard
>>> version-specific fix (I don't think we'd want to backport fb3d824d1a46
>>> with prerequisities). Thanks.
>>
>> I recall seeing+discussing this exact patch already a couple years ago :D
>>
>> Ah, here is the 5.15 version
>>
>> https://lkml.kernel.org/r/20221028075244.3112566-1-songyuanzheng@huawei.com
>>
>> And the 5.10 version
>>
>> https://lore.kernel.org/lkml/20221024094911.3054769-1-songyuanzheng@huawei.com/
>>
>>
>> ... I could have sworn they got applied.
>>
>> ... and in linux-5.10.y I see
>>
>> commit 935a8b6202101d7f58fe9cd11287f9cec0d8dd32
>> Author: Yuanzheng Song <songyuanzheng@huawei.com>
>> Date:   Fri Oct 28 03:07:05 2022 +0000
>>
>>       mm/memory: add non-anonymous page check in the copy_present_page()
>>
>>       The vma->anon_vma of the child process may be NULL because
>>       the entire vma does not contain anonymous pages. In this
>>       case, a BUG will occur when the copy_present_page() passes
>>       a copy of a non-anonymous page of that vma to the
>>       page_add_new_anon_rmap() to set up new anonymous rmap.
>>
>>
>>
>> Maybe you missed that the PageAnon() check is simply a couple of lines
>> further down in there?
> 
> No I was only looking at the 5.15 branch so far, and seems it was never
> applied there, unlike 5.10. Weird. But thanks for the heads up.

Indeed, looks like it never got applied to 5.15 ...

-- 
Cheers,

David / dhildenb