From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed 02 Dec 2015 11:34:07 +0100
Subject: rtmutex: trylock is okay on -RT
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.6/older/patches-4.6.2-rt5.tar.xz

non-RT kernel could deadlock on rt_mutex_trylock() in softirq context. On
-RT we don't run softirqs in IRQ context but in thread context so it is
not a issue here.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/locking/rtmutex.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1478,7 +1478,11 @@ EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
  */
 int __sched rt_mutex_trylock(struct rt_mutex *lock)
 {
+#ifdef CONFIG_PREEMPT_RT_FULL
+	if (WARN_ON(in_irq() || in_nmi()))
+#else
 	if (WARN_ON(in_irq() || in_nmi() || in_serving_softirq()))
+#endif
 		return 0;
 
 	return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
