clockevents: prevent endless loop lockup

The C1E/HPET bug reports on AMDX2/RS690 systems where tracked down to a
too small value of the HPET minumum delta for programming an event.

The clockevents code needs to enforce an interrupt event on the clock event
device in some cases. The enforcement code was stupid and naive, as it just
added the minimum delta to the current time and tried to reprogram the device.
When the minimum delta is too small, then this loops forever.

Add a sanity check. Allow reprogramming to fail 3 times, then print a warning
and double the minimum delta value to make sure, that this does not happen again.
Use the same function for both tick-oneshot and tick-broadcast code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 30 insertions, 6 deletions

diff --git a/kernel/time/tick-oneshot.c b/kernel/time/tick-oneshot.c
index 06595c64b0c..2e35501e61d 100644
--- a/kernel/time/tick-oneshot.c
+++ b/kernel/time/tick-oneshot.c
@@ -25,18 +25,42 @@
 /**
  * tick_program_event internal worker function
  */
-static int __tick_program_event(struct clock_event_device *dev,
-				ktime_t expires, int force)
+int tick_dev_program_event(struct clock_event_device *dev, ktime_t expires,
+			   int force)
 {
 	ktime_t now = ktime_get();
+	int i;
 
-	while (1) {
+	for (i = 0;;) {
 		int ret = clockevents_program_event(dev, expires, now);
 
 		if (!ret || !force)
 			return ret;
+
+		/*
+		 * We tried 2 times to program the device with the given
+		 * min_delta_ns. If that's not working then we double it
+		 * and emit a warning.
+		 */
+		if (++i > 2) {
+			printk(KERN_WARNING "CE: __tick_program_event of %s is "
+			       "stuck %llx %llx\n", dev->name ? dev->name : "?",
+			       now.tv64, expires.tv64);
+			printk(KERN_WARNING
+			       "CE: increasing min_delta_ns %ld to %ld nsec\n",
+			       dev->min_delta_ns, dev->min_delta_ns << 1);
+			WARN_ON(1);
+
+			/* Double the min. delta and try again */
+			if (!dev->min_delta_ns)
+				dev->min_delta_ns = 5000;
+			else
+				dev->min_delta_ns <<= 1;
+			i = 0;
+		}
+
 		now = ktime_get();
-		expires = ktime_add(now, ktime_set(0, dev->min_delta_ns));
+		expires = ktime_add_ns(now, dev->min_delta_ns);
 	}
 }
 
@@ -47,7 +71,7 @@ int tick_program_event(ktime_t expires, int force)
 {
 	struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
 
-	return __tick_program_event(dev, expires, force);
+	return tick_dev_program_event(dev, expires, force);
 }
 
 /**
@@ -71,7 +95,7 @@ void tick_setup_oneshot(struct clock_event_device *newdev,
 {
 	newdev->event_handler = handler;
 	clockevents_set_mode(newdev, CLOCK_EVT_MODE_ONESHOT);
-	__tick_program_event(newdev, next_event, 1);
+	tick_dev_program_event(newdev, next_event, 1);
 }
 
 /**