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authorThomas Gleixner <tglx@linutronix.de>2007-05-29 23:47:39 +0200
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-05-29 18:11:10 -0700
commiteaad084bb0f3a6259e56400cd45d061dbf040600 (patch)
tree34a5f5c3e1a849b035510ee28d5aaffd42a36dcc /kernel/timer.c
parent6e98ee75c3ab99db48ecc0615c2246dc193111a9 (diff)
downloadop-kernel-dev-eaad084bb0f3a6259e56400cd45d061dbf040600.zip
op-kernel-dev-eaad084bb0f3a6259e56400cd45d061dbf040600.tar.gz
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>
Diffstat (limited to 'kernel/timer.c')
-rw-r--r--kernel/timer.c10
1 files changed, 9 insertions, 1 deletions
diff --git a/kernel/timer.c b/kernel/timer.c
index 5ec5490..1a69705 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
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