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    SubjectRe: [PATCH 1/4] cpu_stop: implement stop_cpu[s]()
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    On Tue, 2010-05-04 at 09:03 +0200, Tejun Heo wrote:
    > On 05/04/2010 08:36 AM, Tejun Heo wrote:
    > > On 05/03/2010 03:26 PM, Peter Zijlstra wrote:
    > >> On Thu, 2010-04-22 at 18:09 +0200, Tejun Heo wrote:
    > >>> +static int cpu_stopper_thread(void *data)
    > >>> +{
    > >>> + struct cpu_stopper *stopper = data;
    > >>
    > >> BUG_ON(stopper != __get_cpu_var(cpu_stopper)); ?
    > >
    > > Added.
    >
    > Now that I think more about it, there's a subtle race condition with
    > the above BUG_ON(). Stoppers are prepared by CPU_UP_PREPARE and
    > started by CPU_ONLINE but brought down by CPU_DEAD. IOW, they're
    > allowed to run detached from their designated CPUs between CPU_DYING
    > and CPU_DEAD (the reponsibility of guaranteeing target cpus's onliness
    > is on the callers). So, the above BUG_ON() might trigger spuriously
    > if a cpu goes down after brought online before its cpu_stopper had a
    > chance to pass through the BUG_ON() test.

    Ah indeed. A well, drop it then, its not worth making a more complicated
    test.


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