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 <davem@davemloft.net>

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 <tglx@linutronix.de>
Acked-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/timer.h b/include/linux/timer.h
index e0c5c16..c661710 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -69,6 +69,12 @@ 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:
  */