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    SubjectRe: [RFC PATCH v4 1/9] CPU hotplug: Provide APIs to prevent CPU offline from atomic context
    On 12/12, Oleg Nesterov wrote:
    >
    > On 12/11, Srivatsa S. Bhat wrote:
    > >
    > > IOW, the hotplug readers just increment/decrement their per-cpu refcounts
    > > when no writer is active.
    >
    > plus cli/sti ;) and increment/decrement are atomic.
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    OOPS, sorry I was going to say "adds mb()".

    And when I look at get_online_cpus_atomic() again it uses rmb(). This
    doesn't look correct, we need the full barrier between this_cpu_inc()
    and writer_active().

    At the same time reader_nested_percpu() can be checked before mb().

    Oleg.



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