Messages in this thread | | | Date | Mon, 01 Apr 2013 02:06:17 +0200 | From | Daniel Lezcano <> | Subject | Re: [PATCH] ARM: timer: Shutdown clock event device when stopping local timer |
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On 03/29/2013 10:24 AM, ning.n.jiang@gmail.com wrote: > From: Ning Jiang <ning.n.jiang@gmail.com> > > 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@gmail.com> > ---
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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