2 files changed, 52 insertions, 8 deletions

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 2dc30c59c5fd..2c40ee8f44bd 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1156,6 +1156,29 @@ static void __run_hrtimer(struct hrtimer *timer)
 
 #ifdef CONFIG_HIGH_RES_TIMERS
 
+static int force_clock_reprogram;
+
+/*
+ * After 5 iteration's attempts, we consider that hrtimer_interrupt()
+ * is hanging, which could happen with something that slows the interrupt
+ * such as the tracing. Then we force the clock reprogramming for each future
+ * hrtimer interrupts to avoid infinite loops and use the min_delta_ns
+ * threshold that we will overwrite.
+ * The next tick event will be scheduled to 3 times we currently spend on
+ * hrtimer_interrupt(). This gives a good compromise, the cpus will spend
+ * 1/4 of their time to process the hrtimer interrupts. This is enough to
+ * let it running without serious starvation.
+ */
+
+static inline void
+hrtimer_interrupt_hanging(struct clock_event_device *dev,
+                        ktime_t try_time)
+{
+        force_clock_reprogram = 1;
+        dev->min_delta_ns = (unsigned long)try_time.tv64 * 3;
+        printk(KERN_WARNING "hrtimer: interrupt too slow, "
+                "forcing clock min delta to %lu ns\n", dev->min_delta_ns);
+}
 /*
  * High resolution timer interrupt
  * Called with interrupts disabled
@@ -1165,6 +1188,7 @@ void hrtimer_interrupt(struct clock_event_device *dev)
         struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
         struct hrtimer_clock_base *base;
         ktime_t expires_next, now;
+        int nr_retries = 0;
         int i;
 
         BUG_ON(!cpu_base->hres_active);
@@ -1172,6 +1196,10 @@ void hrtimer_interrupt(struct clock_event_device *dev)
         dev->next_event.tv64 = KTIME_MAX;
 
  retry:
+        /* 5 retries is enough to notice a hang */
+        if (!(++nr_retries % 5))
+                hrtimer_interrupt_hanging(dev, ktime_sub(ktime_get(), now));
+
         now = ktime_get();
 
         expires_next.tv64 = KTIME_MAX;
@@ -1224,7 +1252,7 @@ void hrtimer_interrupt(struct clock_event_device *dev)
 
         /* Reprogramming necessary ? */
         if (expires_next.tv64 != KTIME_MAX) {
-                if (tick_program_event(expires_next, 0))
+                if (tick_program_event(expires_next, force_clock_reprogram))
                         goto retry;
         }
 }
@@ -1578,6 +1606,10 @@ static int __cpuinit hrtimer_cpu_notify(struct notifier_block *self,
                 break;
 
 #ifdef CONFIG_HOTPLUG_CPU
+        case CPU_DYING:
+        case CPU_DYING_FROZEN:
+                clockevents_notify(CLOCK_EVT_NOTIFY_CPU_DYING, &scpu);
+                break;
         case CPU_DEAD:
         case CPU_DEAD_FROZEN:
         {
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 63e05d423a09..21a5ca849514 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -274,6 +274,21 @@ out_bc:
 }
 
 /*
+ * Transfer the do_timer job away from a dying cpu.
+ *
+ * Called with interrupts disabled.
+ */
+static void tick_handover_do_timer(int *cpup)
+{
+        if (*cpup == tick_do_timer_cpu) {
+                int cpu = cpumask_first(cpu_online_mask);
+
+                tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
+                        TICK_DO_TIMER_NONE;
+        }
+}
+
+/*
  * Shutdown an event device on a given cpu:
  *
  * This is called on a life CPU, when a CPU is dead. So we cannot
@@ -297,13 +312,6 @@ static void tick_shutdown(unsigned int *cpup)
                 clockevents_exchange_device(dev, NULL);
                 td->evtdev = NULL;
         }
-        /* Transfer the do_timer job away from this cpu */
-        if (*cpup == tick_do_timer_cpu) {
-                int cpu = cpumask_first(cpu_online_mask);
-
-                tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
-                        TICK_DO_TIMER_NONE;
-        }
         spin_unlock_irqrestore(&tick_device_lock, flags);
 }
 
@@ -357,6 +365,10 @@ static int tick_notify(struct notifier_block *nb, unsigned long reason,
                 tick_broadcast_oneshot_control(reason);
                 break;
 
+        case CLOCK_EVT_NOTIFY_CPU_DYING:
+                tick_handover_do_timer(dev);
+                break;
+
         case CLOCK_EVT_NOTIFY_CPU_DEAD:
                 tick_shutdown_broadcast_oneshot(dev);
                 tick_shutdown_broadcast(dev);