linux-kernel - [PATCH 05/15] alarmtimer: Prevent live lock in alarm

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Date:   Thu,  2 Aug 2018 17:25:20 -0500
From:   Tom Zanussi <tom.zanussi@...ux.intel.com>
To:     linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Cc:     rostedt@...dmis.org, tglx@...utronix.de, C.Emde@...dl.org,
        jkacur@...hat.com, bigeasy@...utronix.de,
        daniel.wagner@...mens.com, julia@...com, stable-rt@...r.kernel.org,
        Tom Zanussi <tom.zanussi@...ux.intel.com>
Subject: [PATCH 05/15] 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>
(cherry picked from commit 51e376c469bf05f32cb1ceb9e39d31bb92f1f6c8)
Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.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 119847b93ba6..5a5e05fc92a3 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -395,7 +395,7 @@ 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);
-- 
2.14.1