From eaad084bb0f3a6259e56400cd45d061dbf040600 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 29 May 2007 23:47:39 +0200 Subject: NOHZ: prevent multiplication overflow - stop timer for huge timeouts get_next_timer_interrupt() returns a delta of (LONG_MAX > 1) in case there is no timer pending. On 64 bit machines this results in a multiplication overflow in tick_nohz_stop_sched_tick(). Reported by: Dave Miller Make the return value a constant and limit the return value to a 32 bit value. When the max timeout value is returned, we can safely stop the tick timer device. The max jiffies delta results in a 12 days timeout for HZ=1000. In the long term the get_next_timer_interrupt() code needs to be reworked to return ktime instead of jiffies, but we have to wait until the last users of the original NO_IDLE_HZ code are converted. Signed-off-by: Thomas Gleixner Acked-off-by: David S. Miller Signed-off-by: Linus Torvalds --- include/linux/timer.h | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'include') diff --git a/include/linux/timer.h b/include/linux/timer.h index e0c5c16c992..c661710d362 100644 --- a/include/linux/timer.h +++ b/include/linux/timer.h @@ -68,6 +68,12 @@ extern int del_timer(struct timer_list * timer); extern int __mod_timer(struct timer_list *timer, unsigned long expires); extern int mod_timer(struct timer_list *timer, unsigned long expires); +/* + * The jiffies value which is added to now, when there is no timer + * in the timer wheel: + */ +#define NEXT_TIMER_MAX_DELTA ((1UL << 30) - 1) + /* * Return when the next timer-wheel timeout occurs (in absolute jiffies), * locks the timer base: -- cgit v1.2.3-18-g5258