[PATCH RT 17/22] alarmtimer: Prevent live lock in alarm_cancel()

[Julia Cartwright]

From: Sebastian Andrzej Siewior <bige...@linutronix.de>

4.9.115-rt94-rc1 stable review patch.
If you have any objection to the inclusion of this patch, let me know.

--- 8< --- 8< --- 8< ---
If alarm_try_to_cancel() requires a retry, then depending on the
priority setting the retry loop might prevent timer callback completion
on RT. Prevent that by waiting for completion on RT, no change for a
non RT kernel.

Cc: stable...@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
(cherry picked from commit 51e376c469bf05f32cb1ceb9e39d31bb92f1f6c8)
Signed-off-by: Julia Cartwright <ju...@ni.com>
---
 kernel/time/alarmtimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index d67ef56ca9bc..61b20a656863 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -407,7 +407,7 @@ int alarm_cancel(struct alarm *alarm)
                int ret = alarm_try_to_cancel(alarm);
                if (ret >= 0)
                        return ret;
-               cpu_relax();
+               hrtimer_wait_for_timer(&alarm->timer);
        }
 }
 EXPORT_SYMBOL_GPL(alarm_cancel);
-- 
2.18.0