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SubjectRe: [PATCH] clockevent: don't remove broadcast device when cpu is dead
On 01/12/2010 09:20 PM, Thomas Gleixner wrote:
> On Thu, 7 Jan 2010, Xiaotian Feng wrote:
>
>> Marc reported BUG during shutdown, after debugging, kernel is trying
>> to remove a broadcast device which mode is CLOCK_EVT_MODE_ONESHOT.
>>
>> The root cause for this bug is that in clockevents_notify,
>> "cpumask_weight(dev->cpumask) == 1" is always true even if dev is a
>
> Why is cpumask_weight(dev->cpumask) == 1 always true when we shutdown
> a non boot cpu ?
>
> The broadcast device is not a per cpu device and the cpumask should
> not only contain the CPU which is shut down !

At least for hpet broadcast dev, it's dev->cpumask is only contain the
CPU which it is initialized from.
And for broadcast device, kernel is using tick_broadcast_mask not
dev->cpumask, right?

>
> The patch is papering over the real problem.
>
> Marc, can you please apply the following debug patch and provide the
> dmesg outputs from boot and shutdown ?
>
> Thanks,
>
> tglx
> ---
>
> Index: linux-2.6-tip/kernel/time/clockevents.c
> ===================================================================
> --- linux-2.6-tip.orig/kernel/time/clockevents.c
> +++ linux-2.6-tip/kernel/time/clockevents.c
> @@ -186,7 +186,7 @@ void clockevents_register_device(struct
> BUG_ON(!dev->cpumask);
>
> raw_spin_lock_irqsave(&clockevents_lock, flags);
> -
> + printk(KERN_ERR "CE register %p %s\n", dev, dev->name);
> list_add(&dev->list,&clockevent_devices);
> clockevents_do_notify(CLOCK_EVT_NOTIFY_ADD, dev);
> clockevents_notify_released();
> @@ -220,6 +220,7 @@ void clockevents_exchange_device(struct
> * released list and do a notify add later.
> */
> if (old) {
> + printk(KERN_INFO "CE Release %p %s\n", old, old->name);
> clockevents_set_mode(old, CLOCK_EVT_MODE_UNUSED);
> list_del(&old->list);
> list_add(&old->list,&clockevents_released);
> @@ -260,6 +261,13 @@ void clockevents_notify(unsigned long re
> list_for_each_entry_safe(dev, tmp,&clockevent_devices, list) {
> if (cpumask_test_cpu(cpu, dev->cpumask)&&
> cpumask_weight(dev->cpumask) == 1) {
> + if (dev->mode != CLOCK_EVT_MODE_UNUSED) {
> + printk(KERN_INFO
> + "CE Remove %p %s bc: %d\n",
> + dev, dev->name,
> + tick_is_broadcast_device(dev));
> + continue;
> + }
> BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED);
> list_del(&dev->list);
> }
> Index: linux-2.6-tip/kernel/time/tick-broadcast.c
> ===================================================================
> --- linux-2.6-tip.orig/kernel/time/tick-broadcast.c
> +++ linux-2.6-tip/kernel/time/tick-broadcast.c
> @@ -72,6 +72,8 @@ int tick_check_broadcast_device(struct c
> (dev->features& CLOCK_EVT_FEAT_C3STOP))
> return 0;
>
> + printk(KERN_INFO "CE set broadcast %p %s\n", dev, dev->name);
> +
> clockevents_exchange_device(NULL, dev);
> tick_broadcast_device.evtdev = dev;
> if (!cpumask_empty(tick_get_broadcast_mask()))
>



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