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    Subject[BUG] cpu-hotplug: Can't offline the CPU with naughty realtime processes

    I found a bug on 2.6.21 cpu-hotplug code.

    When process A on CPU0 try to offline the CPU1 on which the process B,
    realtime process (its task->policy == SCHED_FIFO or SCHED_RR) running
    without sleep or yield, both CPU0 and CPU1 get hang. It's because of
    the following code on __stop_machine_run().

    struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
    unsigned int cpu)
    p = kthread_create(do_stop, &smdata, "kstopmachine");
    if (!IS_ERR(p)) {
    kthread_bind(p, cpu);

    kstopmachine is created, bound to the CPU1, and woken up here, but
    this process can't start to run because reschedule doesn't occur on
    CPU1. Hence CPU0 also be able to run because it's waiting completion
    of CPU1's offline work.


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      Last update: 2007-05-07 12:17    [W:0.065 / U:2.124 seconds]
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