linux-kernel - [PATCH RT 1/3] alarmtimer: Prevent live lock in alarm

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Message-Id: <20180328100746.18668-1-bigeasy@linutronix.de>
Date:   Wed, 28 Mar 2018 12:07:44 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-rt-users@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        stable-rt@...r.kernel.org
Subject: [PATCH RT 1/3] alarmtimer: Prevent live lock in alarm_cancel()

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-rt@...r.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 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 ec09ce9a6012..ede5ef787865 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -429,7 +429,7 @@ 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);
-- 
2.16.3