[PATCH] timers/nohz: Low-res tick handler switch to ONESHOT_STOPPED if tick stops

[Nicholas Piggin]

When tick_nohz_stop_tick() stops the tick, the the clock event device
is not put into ONESHOT_STOPPED mode. This can lead to spurious timer
interrupts with some clock event device drivers that don't shut down
entirely after firing.

Eliminate these by putting the device into ONESHOT_STOPPED mode at
points where it is not being reprogrammed. When there are no timers
active, then tick_program_event() with KTIME_MAX can be used to stop the
device. When there is a timer active, the device can be stopped at the
next tick (any new timer added by timers will reprogram the tick).

Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
 kernel/time/tick-sched.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index d257721c68b8..da1a7efa45a4 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -928,6 +928,8 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int 
cpu)
        if (unlikely(expires == KTIME_MAX)) {
                if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
                        hrtimer_cancel(&ts->sched_timer);
+               else
+                       tick_program_event(KTIME_MAX, 1);
                return;
        }
 
@@ -1364,9 +1366,14 @@ static void tick_nohz_handler(struct clock_event_device 
*dev)
        tick_sched_do_timer(ts, now);
        tick_sched_handle(ts, regs);
 
-       /* No need to reprogram if we are running tickless  */
-       if (unlikely(ts->tick_stopped))
+       if (unlikely(ts->tick_stopped)) {
+               /*
+                * If we are tickless, no need to reprogram, so change the
+                * clock event device to ONESHOT_STOPPED.
+                */
+               tick_program_event(KTIME_MAX, 1);
                return;
+       }
 
        hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
        tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
-- 
2.35.1