[PATCH] tick: prefer a lower rating device only if it's CPU local device

[Sudeep Holla]

Checking the equality of cpumask for both new and old tick device doesn't
ensure that it's CPU local device. This will cause issue if a low rating
clockevent tick device is registered first followed by the registration
of higher rating clockevent tick device.

In such case, clockevents_released list will never get emptied as both
the devices get selected as preferred one and we will loop forever in
clockevents_notify_released.

Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
---
 kernel/time/tick-common.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Hi Thomas,

I am seeing this issue on my Juno devboard, where system wide timers
with rating 300 and 400 are registered in same order and we get stuck in
a loop in clockevents_notify_released. Let me know if this looks sane or
you have any suggestions that I can try out.

Regards,
Sudeep

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 49edc1c4f3e6..78e598334007 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -277,7 +277,8 @@ static bool tick_check_preferred(struct clock_event_device *curdev,
 	 */
 	return !curdev ||
 		newdev->rating > curdev->rating ||
-	       !cpumask_equal(curdev->cpumask, newdev->cpumask);
+	       (!cpumask_equal(curdev->cpumask, newdev->cpumask) &&
+	        !tick_check_percpu(curdev, newdev, smp_processor_id()));
 }

 /*
--
2.7.4