time: add an offline-cpu check in add_timer_on()

Hi everyone,
I think we need a check in the function add_timer_on() to avoid adding a
timer into the timer list of an offline cpu.

This patch fixes this problem in add_timer_on().

---
 kernel/timer.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

index a05817c..6189561 100644
@@ -451,6 +451,7 @@ void add_timer_on(struct timer_list *timer, int cpu)
 	timer_stats_timer_set_start_info(timer);
 	BUG_ON(timer_pending(timer) || !timer->function);
 	spin_lock_irqsave(&base->lock, flags);
+	BUG_ON(cpu_is_offline(cpu));
 	timer_set_base(timer, base);
 	internal_add_timer(base, timer);
 	spin_unlock_irqrestore(&base->lock, flags);

1.5.3.7

No it doesn't -- it will just crash if a caller does that. If it's a real problem then you either need to fix the callers or change add_timer_on() to transparently put it onto another CPU.

I don't think it's a real problem though because CPU offlining does a stop machine and that should take care of most such races.

-Andi

No, the patch is not fixing the problem. It crashes the machine.

Where did you run into this problem ?

Thanks,

tglx

No. CPU offlining does not prevent code to try inserting a timer on a offlined CPU. If there is a real problem with this we need to fix the calling code. We should not insert it somewhere else magically.

Thanks,

tglx