path: root/kernel
diff options
authorjohn stultz <>2009-05-01 13:10:25 -0700
committerThomas Gleixner <>2009-05-02 10:22:27 +0200
commit74a03b69d1b5ce00a568e142ca97e76b7f5239c6 (patch)
tree02bdea43ae6d528dcee97c00c3a8651f8841411a /kernel
parent091438dd5668396328a3419abcbc6591159eb8d1 (diff)
clockevents: prevent endless loop in tick_handle_periodic()
tick_handle_periodic() can lock up hard when a one shot clock event device is used in combination with jiffies clocksource. Avoid an endless loop issue by requiring that a highres valid clocksource be installed before we call tick_periodic() in a loop when using ONESHOT mode. The result is we will only increment jiffies once per interrupt until a continuous hardware clocksource is available. Without this, we can run into a endless loop, where each cycle through the loop, jiffies is updated which increments time by tick_period or more (due to clock steering), which can cause the event programming to think the next event was before the newly incremented time and fail causing tick_periodic() to be called again and the whole process loops forever. [ Impact: prevent hard lock up ] Signed-off-by: John Stultz <> Signed-off-by: Andrew Morton <> Signed-off-by: Thomas Gleixner <> Cc:
Diffstat (limited to 'kernel')
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 21a5ca849514..83c4417b6a3c 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -93,7 +93,17 @@ void tick_handle_periodic(struct clock_event_device *dev)
for (;;) {
if (!clockevents_program_event(dev, next, ktime_get()))
- tick_periodic(cpu);
+ /*
+ * Have to be careful here. If we're in oneshot mode,
+ * before we call tick_periodic() in a loop, we need
+ * to be sure we're using a real hardware clocksource.
+ * Otherwise we could get trapped in an infinite
+ * loop, as the tick_periodic() increments jiffies,
+ * when then will increment time, posibly causing
+ * the loop to trigger again and again.
+ */
+ if (timekeeping_valid_for_hres())
+ tick_periodic(cpu);
next = ktime_add(next, tick_period);