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

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Date:   Fri,  4 May 2018 15:55:14 +0200
From:   Daniel Wagner <wagi@...om.org>
To:     linux-rt-users@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        John Kacur <jkacur@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Daniel Wagner <daniel.wagner@...mens.com>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Julia Cartwright <julia@...com>, stable-rt@...r.kernel.org
Subject: [PATCH RT 1/3] alarmtimer: Prevent live lock in alarm_cancel()

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

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 6fcc367ad531..9d5eac2c9275 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -392,7 +392,7 @@ 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);
-- 
2.14.3