linux-kernel - [PATCH RT 17/22] alarmtimer: Prevent live lock in alarm

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Message-Id: <9288cdf3d1c3fede611a471fcd94f8b9c1b306ed.1533540554.git.julia@ni.com>
Date:   Mon,  6 Aug 2018 04:17:33 -0500
From:   Julia Cartwright <julia@...com>
To:     linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Carsten Emde <C.Emde@...dl.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        John Kacur <jkacur@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Daniel Wagner <daniel.wagner@...mens.com>,
        tom.zanussi@...ux.intel.com, stable-rt@...r.kernel.org
Subject: [PATCH RT 17/22] alarmtimer: Prevent live lock in alarm_cancel()

From: Sebastian Andrzej Siewior <bigeasy@...utronix.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-rt@...r.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
(cherry picked from commit 51e376c469bf05f32cb1ceb9e39d31bb92f1f6c8)
Signed-off-by: Julia Cartwright <julia@...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