For the beginning, about another (but related) minor problem,
debug_smp_processor_id:
/*
* Kernel threads bound to a single CPU can safely use
* smp_processor_id():
*/
This is only true without CONFIG_HOTPLUG_CPU. Otherwise CPU can go away when
the task takes a preemption or sleeps. I think we need #ifndef here.
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".
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().
However, cache_reap() seems to wrongly assume that smp_processor_id() is stable,
this is the second problem.
Is my understanding correct?
Oleg.
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