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SubjectRe: [PATCH] clockevent: don't remove broadcast device when cpu is dead
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 !

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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