smp: Implement kick_all_cpus_sync()

Will replace the misnomed cpu_idle_wait() function which is copied a
gazillion times all over arch/*

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120507175652.049316594@linutronix.de

include/linux/smp.h

@@ -81,6 +81,8 @@ void __smp_call_function_single(int cpuid, struct call_single_data *data,
 int smp_call_function_any(const struct cpumask *mask,
 			  smp_call_func_t func, void *info, int wait);
 
+void kick_all_cpus_sync(void);
+
 /*
  * Generic and arch helpers
  */
@@ -192,6 +194,8 @@ smp_call_function_any(const struct cpumask *mask, smp_call_func_t func,
 	return smp_call_function_single(0, func, info, wait);
 }
 
+static inline void kick_all_cpus_sync(void) {  }
+
 #endif /* !SMP */
 
 /*

kernel/smp.c

@@ -795,3 +795,26 @@ void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
 	}
 }
 EXPORT_SYMBOL(on_each_cpu_cond);
+
+static void do_nothing(void *unused)
+{
+}
+
+/**
+ * kick_all_cpus_sync - Force all cpus out of idle
+ *
+ * Used to synchronize the update of pm_idle function pointer. It's
+ * called after the pointer is updated and returns after the dummy
+ * callback function has been executed on all cpus. The execution of
+ * the function can only happen on the remote cpus after they have
+ * left the idle function which had been called via pm_idle function
+ * pointer. So it's guaranteed that nothing uses the previous pointer
+ * anymore.
+ */
+void kick_all_cpus_sync(void)
+{
+	/* Make sure the change is visible before we kick the cpus */
+	smp_mb();
+	smp_call_function(do_nothing, NULL, 1);
+}
+EXPORT_SYMBOL_GPL(kick_all_cpus_sync);