[PATCH] cpu hotplug: make [un]register_cpu_notifier init time only

CPUs come online only at init time (unless CONFIG_HOTPLUG_CPU is defined).
So, cpu_notifier functionality need to be available only at init time.

This patch makes register_cpu_notifier() available only at init time, unless
CONFIG_HOTPLUG_CPU is defined.

This patch exports register_cpu_notifier() and unregister_cpu_notifier() only
if CONFIG_HOTPLUG_CPU is defined.

Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Cc: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/cpufreq/cpufreq.c

@@ -1497,7 +1497,8 @@ int cpufreq_update_policy(unsigned int cpu)
 }
 EXPORT_SYMBOL(cpufreq_update_policy);
 
-static int __cpuinit cpufreq_cpu_callback(struct notifier_block *nfb,
+#ifdef CONFIG_HOTPLUG_CPU
+static int cpufreq_cpu_callback(struct notifier_block *nfb,
 					unsigned long action, void *hcpu)
 {
 	unsigned int cpu = (unsigned long)hcpu;
@@ -1536,6 +1537,7 @@ static struct notifier_block cpufreq_cpu_notifier =
 {
     .notifier_call = cpufreq_cpu_callback,
 };
+#endif /* CONFIG_HOTPLUG_CPU */
 
 /*********************************************************************
  *               REGISTER / UNREGISTER CPUFREQ DRIVER                *
@@ -1596,7 +1598,7 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
 	}
 
 	if (!ret) {
-		register_cpu_notifier(&cpufreq_cpu_notifier);
+		register_hotcpu_notifier(&cpufreq_cpu_notifier);
 		dprintk("driver %s up and running\n", driver_data->name);
 		cpufreq_debug_enable_ratelimit();
 	}
@@ -1628,7 +1630,7 @@ int cpufreq_unregister_driver(struct cpufreq_driver *driver)
 	dprintk("unregistering driver %s\n", driver->name);
 
 	sysdev_driver_unregister(&cpu_sysdev_class, &cpufreq_sysdev_driver);
-	unregister_cpu_notifier(&cpufreq_cpu_notifier);
+	unregister_hotcpu_notifier(&cpufreq_cpu_notifier);
 
 	spin_lock_irqsave(&cpufreq_driver_lock, flags);
 	cpufreq_driver = NULL;

drivers/cpufreq/cpufreq_stats.c

@@ -350,7 +350,7 @@ __init cpufreq_stats_init(void)
 		return ret;
 	}
 
-	register_cpu_notifier(&cpufreq_stat_cpu_notifier);
+	register_hotcpu_notifier(&cpufreq_stat_cpu_notifier);
 	lock_cpu_hotplug();
 	for_each_online_cpu(cpu) {
 		cpufreq_stat_cpu_callback(&cpufreq_stat_cpu_notifier, CPU_ONLINE,
@@ -368,7 +368,7 @@ __exit cpufreq_stats_exit(void)
 			CPUFREQ_POLICY_NOTIFIER);
 	cpufreq_unregister_notifier(&notifier_trans_block,
 			CPUFREQ_TRANSITION_NOTIFIER);
-	unregister_cpu_notifier(&cpufreq_stat_cpu_notifier);
+	unregister_hotcpu_notifier(&cpufreq_stat_cpu_notifier);
 	lock_cpu_hotplug();
 	for_each_online_cpu(cpu) {
 		cpufreq_stat_cpu_callback(&cpufreq_stat_cpu_notifier, CPU_DEAD,

include/linux/cpu.h

@@ -41,7 +41,13 @@ struct notifier_block;
 #ifdef CONFIG_SMP
 /* Need to know about CPUs going up/down? */
 extern int register_cpu_notifier(struct notifier_block *nb);
+#ifdef CONFIG_HOTPLUG_CPU
 extern void unregister_cpu_notifier(struct notifier_block *nb);
+#else
+static inline void unregister_cpu_notifier(struct notifier_block *nb)
+{
+}
+#endif
 extern int current_in_cpu_hotplug(void);
 
 int cpu_up(unsigned int cpu);

kernel/cpu.c

@@ -18,7 +18,7 @@
 /* This protects CPUs going up and down... */
 static DEFINE_MUTEX(cpucontrol);
 
-static BLOCKING_NOTIFIER_HEAD(cpu_chain);
+static __cpuinitdata BLOCKING_NOTIFIER_HEAD(cpu_chain);
 
 #ifdef CONFIG_HOTPLUG_CPU
 static struct task_struct *lock_cpu_hotplug_owner;
@@ -69,10 +69,13 @@ EXPORT_SYMBOL_GPL(lock_cpu_hotplug_interruptible);
 #endif	/* CONFIG_HOTPLUG_CPU */
 
 /* Need to know about CPUs going up/down? */
-int register_cpu_notifier(struct notifier_block *nb)
+int __cpuinit register_cpu_notifier(struct notifier_block *nb)
 {
 	return blocking_notifier_chain_register(&cpu_chain, nb);
 }
+
+#ifdef CONFIG_HOTPLUG_CPU
+
 EXPORT_SYMBOL(register_cpu_notifier);
 
 void unregister_cpu_notifier(struct notifier_block *nb)
@@ -81,7 +84,6 @@ void unregister_cpu_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL(unregister_cpu_notifier);
 
-#ifdef CONFIG_HOTPLUG_CPU
 static inline void check_for_tasks(int cpu)
 {
 	struct task_struct *p;