Re: [PATCH] clockevent: don't remove broadcast device when cpu isdead

From: Xiaotian Feng
Date: Tue Jan 12 2010 - 20:49:13 EST

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 ?



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

raw_spin_lock_irqsave(&clockevents_lock, flags);
+ printk(KERN_ERR "CE register %p %s\n", dev, dev->name);
clockevents_do_notify(CLOCK_EVT_NOTIFY_ADD, dev);
@@ -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);
@@ -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;
+ }
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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