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    SubjectRe: Question about synchronize_sched_expedited()
    Hello, Paul.

    On 10/25/2010 05:43 PM, Paul E. McKenney wrote:
    > Hello, Tejun,
    > I was taking another look at synchronize_sched_expedited(), and was
    > concerned about the scenario listed out in the following commit.
    > Is this scenario a real problem, or am I missing the synchronization
    > that makes it safe?
    > (If my concerns are valid, I should also be able to change this
    > to non-atomically increment synchronize_sched_expedited_count, but
    > one step at a time...)

    I think your concern is valid and this can happen w/o preemption given
    enough cpus and perfect timing. Was the original code free from this

    IMHO the counter based mechanism is a bit too difficult to ponder and
    verify. Can we do more conventional double queueing (ie. flipping
    pending and executing queues so that multiple sync calls can get
    coalesced while another one is in progress)? That's what the code is
    trying to achieve anyway, right?



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