linux-kernel - Re: [PATCH] clockevent: don't remove broadcast device when cpu is dead

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Date:	Wed, 13 Jan 2010 09:48:40 +0800
From:	Xiaotian Feng <dfeng@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	linux-kernel@...r.kernel.org, Magnus Damm <damm@...l.co.jp>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>
Subject: Re: [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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