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/time/tick-sched.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) (limited to 'kernel/time') diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 3e7ebc4646b..52db9e3c526 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -247,6 +247,21 @@ void tick_nohz_stop_sched_tick(void) if (cpu == tick_do_timer_cpu) tick_do_timer_cpu = -1; + ts->idle_sleeps++; + + /* + * delta_jiffies >= NEXT_TIMER_MAX_DELTA signals that + * there is no timer pending or at least extremly far + * into the future (12 days for HZ=1000). In this case + * we simply stop the tick timer: + */ + if (unlikely(delta_jiffies >= NEXT_TIMER_MAX_DELTA)) { + ts->idle_expires.tv64 = KTIME_MAX; + if (ts->nohz_mode == NOHZ_MODE_HIGHRES) + hrtimer_cancel(&ts->sched_timer); + goto out; + } + /* * calculate the expiry time for the next timer wheel * timer @@ -254,7 +269,6 @@ void tick_nohz_stop_sched_tick(void) expires = ktime_add_ns(last_update, tick_period.tv64 * delta_jiffies); ts->idle_expires = expires; - ts->idle_sleeps++; if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { hrtimer_start(&ts->sched_timer, expires, -- cgit v1.2.3