Messages in this thread | | | Date | Mon, 29 Jan 2007 08:54:36 -0800 (PST) | From | Christoph Lameter <> | Subject | Re: slab: start_cpu_timer/cache_reap CONFIG_HOTPLUG_CPU problems |
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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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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