On Mon, 29 Jan 2007, Oleg Nesterov wrote:
> Now,
> static void __devinit start_cpu_timer(int cpu)
> {
> struct delayed_work *reap_work = &per_cpu(reap_work, cpu);
>
> if (keventd_up() && reap_work->work.func == NULL) {
> init_reap_node(cpu);
> INIT_DELAYED_WORK(reap_work, cache_reap);
> schedule_delayed_work_on(cpu, reap_work,
> __round_jiffies_relative(HZ,
> cpu));
> }
> }
>
> This is wrong. Suppose we have a CPU_UP,CPU_DOWN,CPU_UP sequence. The last
> CPU_UP will not restart a per-cpu "cache_reap timer".
Why?
> With or without recent changes, it is possible that work->func() will run on
> another CPU (not that to which it was submitted) if CPU goes down. In fact,
> this can happen while work->func() is running, so even smp_processor_id()
> is not safe to use in work->func().
But the work func was scheduled by schedule_delayed_work_on(). Isnt that a
general problem with schedule_delayed_work_on() and keventd?
> However, cache_reap() seems to wrongly assume that smp_processor_id() is
> stable,
> this is the second problem.
>
> Is my understanding correct?
cache_reap assumes that the processor id is stable based on the kevent
thread being pinned to a processor.
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