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>
diff --git a/kernel/timer.c b/kernel/timer.c
index 5ec5490f..1a69705 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -666,7 +666,7 @@
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 @@
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
