Add on_cpu_single

Call a function on a target CPU but do the right thing when 
we're already on that CPU. That's the main difference from smp_call_function_single
which does the wrong thing in this case (erroring out)

Another advantage is that it is also defined for the UP case, avoiding
some ifdefs.

I also dropped retry (which never did anything) and wait (because the on
current cpu case will always wait)
Signed-off-by: Andi Kleen <ak@suse.de>

---
 include/linux/smp.h |   22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

Index: linux/include/linux/smp.h
===================================================================
--- linux.orig/include/linux/smp.h
+++ linux/include/linux/smp.h
@@ -135,4 +135,26 @@ static inline int smp_call_function_sing
 
 void smp_setup_processor_id(void);
 
+#ifdef CONFIG_SMP
+/* Similar to smp_call_function_single, but DTRT when we're already
+   on the right CPU. */
+static inline void on_cpu_single(int cpu, void (*func)(void *), void *info)
+{
+	int me = get_cpu();
+	if (cpu == me) {
+		func(info);
+		put_cpu();
+	} else {
+		put_cpu();
+		/* wait is forced on because the me==cpu case above will always wait */
+		smp_call_function_single(cpu, func, info, 0, 1);
+	}
+}
+#else
+static inline void on_cpu_single(int cpu, void (*func)(void *), void *info)
+{
+	func(info);
+}
+#endif
+
 #endif /* __LINUX_SMP_H */