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| author | Thomas Gleixner <tglx@linutronix.de> | 2007-05-29 23:47:39 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-05-29 18:11:10 -0700 |
| commit | eaad084bb0f3a6259e56400cd45d061dbf040600 (patch) | |
| tree | 34a5f5c3e1a849b035510ee28d5aaffd42a36dcc /kernel | |
| parent | 6e98ee75c3ab99db48ecc0615c2246dc193111a9 (diff) | |
| download | lwn-eaad084bb0f3a6259e56400cd45d061dbf040600.tar.gz lwn-eaad084bb0f3a6259e56400cd45d061dbf040600.zip | |
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')
| -rw-r--r-- | kernel/time/tick-sched.c | 16 | ||||
| -rw-r--r-- | kernel/timer.c | 10 |
2 files changed, 24 insertions, 2 deletions
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 3e7ebc4646b7..52db9e3c526e 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, 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 |