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    SubjectRe: CPU hotplug broken in 2.6.8-rc2 ?
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    On Mon, 2004-08-02 at 15:26, Nathan Lynch wrote:
    > On Mon, 2004-08-02 at 14:38, Nathan Lynch wrote:
    > > Could you try on 2.6.8-rc2-mm2 along with this patch? Vatsa had a patch
    > > go in that should prevent the crash you are seeing -- the patch below is
    > > needed to prevent the same crash in the offline case. This check used
    > > to be in load_balance and some other scheduler functions, iirc; does
    > > anyone know why they were removed?
    >
    > Er, I meant to put the check in rebalance_tick, not load_balance.
    >
    > However, after a few minutes with this, I hit the BUG_ON in the CPU_DEAD
    > case in migration_call; not sure whether this is a separate issue.

    So, with the cpu_is_offline check in rebalance_tick on top of
    2.6.8-rc2-mm2, this is the BUG_ON in migration_call I tend to hit while
    hotplugging cpus as quickly as possible while running make -j 40:

    case CPU_DEAD:
    migrate_all_tasks(cpu);
    rq = cpu_rq(cpu);
    kthread_stop(rq->migration_thread);
    rq->migration_thread = NULL;
    /* Idle task back to normal (off runqueue, low prio) */
    rq = task_rq_lock(rq->idle, &flags);
    deactivate_task(rq->idle, rq);
    rq->idle->static_prio = MAX_PRIO;
    __setscheduler(rq->idle, SCHED_NORMAL, 0);
    task_rq_unlock(rq, &flags);
    BUG_ON(rq->nr_running != 0);

    I can reproduce this on both ppc64 and i386. Does anyone know why this
    is happening?

    If I remove the BUG_ON, things seem to go ok, but I doubt that's the
    right thing to do.

    Nathan


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