On 03/29/2013 10:24 AM, ning.n.jiang@xxxxxxxxx wrote:
> From: Ning Jiang <ning.n.jiang@xxxxxxxxx>
>
> Currently there are two problems when we try to stop local timer.
> First, it calls set_mode function directly so mode state is not
> updated for the clock event device. Second, it makes the device
> unused instead of shutdown.
>
> A subtle error will happen because of it. When a cpu is plugged out
> it will stop the local timer. It will call tick_nohz_idle_enter()
> in idle thread afterwards. It will cancel the sched timer and try
> to reprogram the next event. This is wrong since the local timer
> is supposed to be stopped.
>
> The right way to stop the local timer is to shutdown it by calling
> clockevents_set_mode(). Thus when we try to reprogram the clock
> event device, it will return directly without doing anything since
> the clock mode is CLOCK_EVT_MODE_SHUTDOWN.
>
> Signed-off-by: Ning Jiang <ning.n.jiang@xxxxxxxxx>
> ---
Don't you see a kernel BUG with this patch ?
In the clockevents code, there is:
/**
* clockevents_notify - notification about relevant events
*/
void clockevents_notify(unsigned long reason, void *arg)
{
...
case CLOCK_EVT_NOTIFY_CPU_DEAD:
...
cpu = *((int *)arg);
list_for_each_entry_safe(dev, tmp, &clockevent_devices,
list) {
if (cpumask_test_cpu(cpu, dev->cpumask) &&
cpumask_weight(dev->cpumask) == 1 &&
!tick_is_broadcast_device(dev)) {
BUG_ON(dev->mode !=
CLOCK_EVT_MODE_UNUSED);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
list_del(&dev->list);
}
}
break;
...
}
This is called triggered from hrtimer_cpu_notify with the CPU_DEAD event.
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