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 --- kernel/timer.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'kernel/timer.c') diff --git a/kernel/timer.c b/kernel/timer.c index 5ec5490f8d85..1a69705c2fb9 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -666,7 +666,7 @@ static inline void __run_timers(tvec_base_t *base) static unsigned long __next_timer_interrupt(tvec_base_t *base) { unsigned long timer_jiffies = base->timer_jiffies; - unsigned long expires = timer_jiffies + (LONG_MAX >> 1); + unsigned long expires = timer_jiffies + NEXT_TIMER_MAX_DELTA; int index, slot, array, found = 0; struct timer_list *nte; tvec_t *varray[4]; @@ -752,6 +752,14 @@ static unsigned long cmp_next_hrtimer_event(unsigned long now, tsdelta = ktime_to_timespec(hr_delta); delta = timespec_to_jiffies(&tsdelta); + + /* + * Limit the delta to the max value, which is checked in + * tick_nohz_stop_sched_tick(): + */ + if (delta > NEXT_TIMER_MAX_DELTA) + delta = NEXT_TIMER_MAX_DELTA; + /* * Take rounding errors in to account and make sure, that it * expires in the next tick. Otherwise we go into an endless -- cgit v1.2.3