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    SubjectRe: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM
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    On Fri, 2011-05-27 at 20:53 +0530, Santosh Shilimkar wrote:
    > Peter,
    >
    > On 5/26/2011 10:53 PM, Peter Zijlstra wrote:
    > > On Thu, 2011-05-26 at 19:17 +0200, Peter Zijlstra wrote:
    > >> On Thu, 2011-05-26 at 19:04 +0200, Oleg Nesterov wrote:
    > >>> On 05/26, Peter Zijlstra wrote:
    > >>>>
    > >>>> @@ -2636,7 +2636,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
    > >>>> * to spin on ->on_cpu if p is current, since that would
    > >>>> * deadlock.
    > >>>> */
    > >>>> - if (p == current) {
    > >>>> + if (cpu == smp_processor_id()) {
    > >>>> + p->sched_contributes_to_load = 0;
    > >>>> ttwu_queue(p, cpu);
    > >>>
    > >>> Btw. I do not pretend I really understand se->vruntime, but in this
    > >>> case we are doing enqueue_task() without ->task_waking(), however we
    > >>> pass ENQUEUE_WAKING. Is it correct?
    > >>
    > >> No its not, that's the thing that I got wrong the first time and caused
    > >> these pauses.
    > >
    > > We'd end up with something like the below, which isn't too different
    > > from what I've now got queued.
    > >
    > > It has the extra cpu == smp_processor_id() check, but I'm not sure this
    > > whole case is worth the trouble. I could go stick some counters in to
    > > verify how often all this happens I guess.
    > >
    > Are you planning send version of this patch for stable .39
    > too ?

    .39 is fine, as the ttwu() changes only appeared in mainline during the
    current merge window.

    Cheers,

    M.
    --
    Reality is an implementation detail.




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