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

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Date:   Fri,  2 Jun 2023 21:43:47 +0000
From:   SeongJae Park <sj@...nel.org>
To:     SeongJae Park <sj@...nel.org>
Cc:     Ryan Roberts <ryan.roberts@....com>, 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 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!

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


Thanks,
SJ

> 
> 
> Thanks,
> SJ
>