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    SubjectRe: [PATCH] mm: change memcg->oom_group access with atomic operations
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    > On Feb 21, 2023, at 13:17, Roman Gushchin <roman.gushchin@linux.dev> wrote:
    >
    >> On Feb 20, 2023, at 3:06 PM, Shakeel Butt <shakeelb@google.com> wrote:
    >>
    >> On Mon, Feb 20, 2023 at 01:09:44PM -0800, Roman Gushchin wrote:
    >>>> On Mon, Feb 20, 2023 at 11:16:38PM +0800, Yue Zhao wrote:
    >>>> The knob for cgroup v2 memory controller: memory.oom.group
    >>>> will be read and written simultaneously by user space
    >>>> programs, thus we'd better change memcg->oom_group access
    >>>> with atomic operations to avoid concurrency problems.
    >>>>
    >>>> Signed-off-by: Yue Zhao <findns94@gmail.com>
    >>>
    >>> Hi Yue!
    >>>
    >>> I'm curious, have any seen any real issues which your patch is solving?
    >>> Can you, please, provide a bit more details.
    >>>
    >>
    >> IMHO such details are not needed. oom_group is being accessed
    >> concurrently and one of them can be a write access. At least
    >> READ_ONCE/WRITE_ONCE is needed here.
    >
    > Needed for what?
    >
    > I mean it’s obviously not a big deal to put READ_ONCE()/WRITE_ONCE() here, but I struggle to imagine a scenario when it will make any difference. IMHO it’s easier to justify a proper atomic operation here, even if it’s most likely an overkill.
    >
    > My question is very simple: the commit log mentions “… to avoid concurrency problems”, so I wonder what problems are these.

    I think there is no difference in the assembly code between them in most
    cases. The only intention that I can think of is to avoid the potential
    complaint (data race) emitted by KCSAN.

    >
    > Also there are other similar cgroup interfaces without READ_ONCE()/WRITE_ONCE().

    If we decide to fix, then we should fix all.

    Thanks.

    >
    > Thanks!


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