clockevents: Update clockevents device next_event on stop

clockevent_device::next_event holds the next timer event of a clock event
device. The value is updated in clockevents_program_event(), i.e. when the
hardware timer is armed for the next expiry.

When there are no software timers armed on a CPU, the corresponding per CPU
clockevent device is brought into ONESHOT_STOPPED state, but
clockevent_device::next_event is not updated, because
clockevents_program_event() is not called.

So the content of clockevent_device::next_event is stale, which is not an
issue when real hardware is used. But the hrtimer broadcast device relies
on that information and the stale value causes spurious wakeups.

Update clockevent_device::next_event to KTIME_MAX when it has been brought
into ONESHOT_STOPPED state to avoid spurious wakeups. This reflects the
proper expiry time of the stopped timer: infinity.

[ tglx: Massaged changelog ]
Signed-off-by: NPrasad Sodagudi <psodagud@codeaurora.org>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: viresh.kumar@linaro.org
Link: https://lkml.kernel.org/r/1509043042-32486-1-git-send-email-psodagud@codeaurora.org

kernel/time/tick-oneshot.c

@@ -33,6 +33,7 @@ int tick_program_event(ktime_t expires, int force)
 		 * We don't need the clock event device any more, stop it.
 		 */
 		clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT_STOPPED);
+		dev->next_event = KTIME_MAX;
 		return 0;
 	}