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References: <20230602092949.545577-1-ryan.roberts@arm.com> <20230602092949.545577-3-ryan.roberts@arm.com>
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From:   Yu Zhao <yuzhao@google.com>
Date:   Fri, 2 Jun 2023 10:35:08 -0600
Message-ID: <CAOUHufb5R_+eMxM28WWxXubPzUO4+c_1UHoXVAcWsKEyG1ndAQ@mail.gmail.com>
Subject: Re: [PATCH v3 2/4] mm/damon/ops-common: atomically test and clear
 young on ptes and pmds
To:     Ryan Roberts <ryan.roberts@arm.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        SeongJae Park <sj@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Lorenzo Stoakes <lstoakes@gmail.com>,
        Uladzislau Rezki <urezki@gmail.com>, Zi Yan <ziy@nvidia.com>,
        Mike Rapoport <rppt@kernel.org>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, damon@lists.linux.dev
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On Fri, Jun 2, 2023 at 3:30=E2=80=AFAM Ryan Roberts <ryan.roberts@arm.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 memo=
ry address spaces").

Just to double check: was "Cc: stable@vger.kernel.org" overlooked or
deemed unnecessary?

> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: SeongJae Park <sj@kernel.org>
> Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>