From 6ff7041dbfeb3bd7dfe9aa67275c21199ef760d6 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 10 Jul 2009 14:57:05 +0200 Subject: hrtimer: Fix migration expiry check The timer migration expiry check should prevent the migration of a timer to another CPU when the timer expires before the next event is scheduled on the other CPU. Migrating the timer might delay it because we can not reprogram the clock event device on the other CPU. But the code implementing that check has two flaws: - for !HIGHRES the check compares the expiry value with the clock events device expiry value which is wrong for CLOCK_REALTIME based timers. - the check is racy. It holds the hrtimer base lock of the target CPU, but the clock event device expiry value can be modified nevertheless, e.g. by an timer interrupt firing. The !HIGHRES case is easy to fix as we can enqueue the timer on the cpu which was selected by the load balancer. It runs the idle balancing code once per jiffy anyway. So the maximum delay for the timer is the same as when we keep the tick on the current cpu going. In the HIGHRES case we can get the next expiry value from the hrtimer cpu_base of the target CPU and serialize the update with the cpu_base lock. This moves the lock section in hrtimer_interrupt() so we can set next_event to KTIME_MAX while we are handling the expired timers and set it to the next expiry value after we handled the timers under the base lock. While the expired timers are processed timer migration is blocked because the expiry time of the timer is always <= KTIME_MAX. Also remove the now useless clockevents_get_next_event() function. Signed-off-by: Thomas Gleixner --- kernel/time/clockevents.c | 11 ----------- 1 file changed, 11 deletions(-) (limited to 'kernel/time') diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c index 1ad6dd46111..a6dcd67b041 100644 --- a/kernel/time/clockevents.c +++ b/kernel/time/clockevents.c @@ -254,15 +254,4 @@ void clockevents_notify(unsigned long reason, void *arg) spin_unlock(&clockevents_lock); } EXPORT_SYMBOL_GPL(clockevents_notify); - -ktime_t clockevents_get_next_event(int cpu) -{ - struct tick_device *td; - struct clock_event_device *dev; - - td = &per_cpu(tick_cpu_device, cpu); - dev = td->evtdev; - - return dev->next_event; -} #endif -- cgit v1.2.3 From 79ef2bb01445400def20c7993b27fbcad27ca95f Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sun, 19 Jul 2009 17:09:12 +0200 Subject: clocksource: Prevent NULL pointer dereference Writing a zero length string to sys/.../current_clocksource will cause a NULL pointer dereference if the clock events system is in one shot (highres or nohz) mode. Pointed-out-by: Dan Carpenter LKML-Reference: Signed-off-by: Thomas Gleixner --- kernel/time/clocksource.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/time') diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 592bf584d1d..7466cb81125 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -513,7 +513,7 @@ static ssize_t sysfs_override_clocksource(struct sys_device *dev, * Check to make sure we don't switch to a non-highres capable * clocksource if the tick code is in oneshot mode (highres or nohz) */ - if (tick_oneshot_mode_active() && + if (tick_oneshot_mode_active() && ovr && !(ovr->flags & CLOCK_SOURCE_VALID_FOR_HRES)) { printk(KERN_WARNING "%s clocksource is not HRT compatible. " "Cannot switch while in HRT/NOHZ mode\n", ovr->name); -- cgit v1.2.3