linux-kernel - Re: [PATCH v3 2/4] mm/damon/ops-common: atomically test and clear young on ptes and pmds

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Message-ID: <c87d4b69-0971-2faf-9d10-615e3264b131@arm.com>
Date:   Sat, 3 Jun 2023 19:20:34 +0100
From:   Ryan Roberts <ryan.roberts@....com>
To:     SeongJae Park <sj@...nel.org>
Cc:     Yu Zhao <yuzhao@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Uladzislau Rezki <urezki@...il.com>, Zi Yan <ziy@...dia.com>,
        Mike Rapoport <rppt@...nel.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, damon@...ts.linux.dev
Subject: Re: [PATCH v3 2/4] mm/damon/ops-common: atomically test and clear
 young on ptes and pmds

On 02/06/2023 22:43, SeongJae Park wrote:
> On Fri, 2 Jun 2023 19:15:01 +0000 SeongJae Park <sj@...nel.org> wrote:
> 
>> Hi Ryan,
>>
>> On Fri, 2 Jun 2023 18:14:25 +0100 Ryan Roberts <ryan.roberts@....com> wrote:
>>
>>> On 02/06/2023 17:35, Yu Zhao wrote:
>>>> On Fri, Jun 2, 2023 at 3:30 AM Ryan Roberts <ryan.roberts@....com> wrote:
>>>>>
>>>>> It is racy to non-atomically read a pte, then clear the young bit, then
>>>>> write it back as this could discard dirty information. Further, it is
>>>>> bad practice to directly set a pte entry within a table. Instead
>>>>> clearing young must go through the arch-provided helper,
>>>>> ptep_test_and_clear_young() to ensure it is modified atomically and to
>>>>> give the arch code visibility and allow it to check (and potentially
>>>>> modify) the operation.
>>>>>
>>>>> Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces").
>>>>
>>>> Just to double check: was "Cc: stable@...r.kernel.org" overlooked or
>>>> deemed unnecessary?
>>>
>>> It was overlooked - incompetance strikes again! I was intending to cc the
>>> whole series.
>>
>> Not the whole patches in this series but only this patch is intended to be
>> merged in stable series, right?  If I'm not wrong, you could add
>> 'Cc: <stable@...r.kernel.org>' tag here[1] when resending, to let stable kernel
>> maintainers easily understand exactly what patches should be merged in the
>> stable kernels.  So, you wouldn't need to touch coverletter or cc whole series
>> but only this one.
>>
>> [1] https://www.kernel.org/doc/html/v4.10/process/stable-kernel-rules.html
> 
> And I just found Andrew added the tag while adding this to the -mm queue.
> Thank you, Andrew!

Yes indeed - thanks for fixing that up for me, Andrew!

> 
> [1] https://lore.kernel.org/mm-commits/20230602205509.9DFBDC433D2@smtp.kernel.org/
> 
> 
> Thanks,
> SJ
> 
>>
>>
>> Thanks,
>> SJ
>>