Subject: rt: Introduce cpu_chill()
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 07 Mar 2012 20:51:03 +0100

Retry loops on RT might loop forever when the modifying side was
preempted. Add cpu_chill() to replace cpu_relax(). cpu_chill()
defaults to cpu_relax() for non RT. On RT it puts the looping task to
sleep for a tick so the preempted task can make progress.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
---
 include/linux/delay.h |    6 ++++++
 1 file changed, 6 insertions(+)

Index: linux-stable/include/linux/delay.h
===================================================================
--- linux-stable.orig/include/linux/delay.h
+++ linux-stable/include/linux/delay.h
@@ -52,4 +52,10 @@ static inline void ssleep(unsigned int s
 	msleep(seconds * 1000);
 }
 
+#ifdef CONFIG_PREEMPT_RT_FULL
+# define cpu_chill()	msleep(1)
+#else
+# define cpu_chill()	cpu_relax()
+#endif
+
 #endif /* defined(_LINUX_DELAY_H) */