From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 2 Dec 2015 11:34:07 +0100
Subject: rtmutex: trylock is okay on -RT
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 343a8d3b8f9797a1d3fc212016b58cb56232c375
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

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>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 kernel/locking/rtmutex.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1551,7 +1551,11 @@ int __sched rt_mutex_trylock(struct rt_m
 {
 	int ret;
 
+#ifdef CONFIG_PREEMPT_RT_FULL
+	if (WARN_ON_ONCE(in_irq() || in_nmi()))
+#else
 	if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
+#endif
 		return 0;
 
 	ret = rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);