3 files changed, 48 insertions, 3 deletions

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index bfda3f7f0716..a96ec9ab3454 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -31,7 +31,7 @@ DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
  */
 ktime_t tick_next_period;
 ktime_t tick_period;
-static int tick_do_timer_cpu = -1;
+int tick_do_timer_cpu __read_mostly = -1;
 DEFINE_SPINLOCK(tick_device_lock);
 
 /*
@@ -295,6 +295,12 @@ 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 = first_cpu(cpu_online_map);
+
+                tick_do_timer_cpu = (cpu != NR_CPUS) ? cpu : -1;
+        }
         spin_unlock_irqrestore(&tick_device_lock, flags);
 }
 
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index c9d203bde518..bb13f2724905 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -5,6 +5,7 @@ DECLARE_PER_CPU(struct tick_device, tick_cpu_device);
 extern spinlock_t tick_device_lock;
 extern ktime_t tick_next_period;
 extern ktime_t tick_period;
+extern int tick_do_timer_cpu __read_mostly;
 
 extern void tick_setup_periodic(struct clock_event_device *dev, int broadcast);
 extern void tick_handle_periodic(struct clock_event_device *dev);
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 51556b95f60f..f4fc867f467d 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -221,6 +221,18 @@ void tick_nohz_stop_sched_tick(void)
                         ts->tick_stopped = 1;
                         ts->idle_jiffies = last_jiffies;
                 }
+
+                /*
+                 * If this cpu is the one which updates jiffies, then
+                 * give up the assignment and let it be taken by the
+                 * cpu which runs the tick timer next, which might be
+                 * this cpu as well. If we don't drop this here the
+                 * jiffies might be stale and do_timer() never
+                 * invoked.
+                 */
+                if (cpu == tick_do_timer_cpu)
+                        tick_do_timer_cpu = -1;
+
                 /*
                  * calculate the expiry time for the next timer wheel
                  * timer
@@ -338,12 +350,24 @@ static void tick_nohz_handler(struct clock_event_device *dev)
 {
         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
         struct pt_regs *regs = get_irq_regs();
+        int cpu = smp_processor_id();
         ktime_t now = ktime_get();
 
         dev->next_event.tv64 = KTIME_MAX;
 
+        /*
+         * Check if the do_timer duty was dropped. We don't care about
+         * concurrency: This happens only when the cpu in charge went
+         * into a long sleep. If two cpus happen to assign themself to
+         * this duty, then the jiffies update is still serialized by
+         * xtime_lock.
+         */
+        if (unlikely(tick_do_timer_cpu == -1))
+                tick_do_timer_cpu = cpu;
+
         /* Check, if the jiffies need an update */
-        tick_do_update_jiffies64(now);
+        if (tick_do_timer_cpu == cpu)
+                tick_do_update_jiffies64(now);
 
         /*
          * When we are idle and the tick is stopped, we have to touch
@@ -431,9 +455,23 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
         struct hrtimer_cpu_base *base = timer->base->cpu_base;
         struct pt_regs *regs = get_irq_regs();
         ktime_t now = ktime_get();
+        int cpu = smp_processor_id();
+
+#ifdef CONFIG_NO_HZ
+        /*
+         * Check if the do_timer duty was dropped. We don't care about
+         * concurrency: This happens only when the cpu in charge went
+         * into a long sleep. If two cpus happen to assign themself to
+         * this duty, then the jiffies update is still serialized by
+         * xtime_lock.
+         */
+        if (unlikely(tick_do_timer_cpu == -1))
+                tick_do_timer_cpu = cpu;
+#endif
 
         /* Check, if the jiffies need an update */
-        tick_do_update_jiffies64(now);
+        if (tick_do_timer_cpu == cpu)
+                tick_do_update_jiffies64(now);
 
         /*
          * Do not call, when we are not in irq context and have