[PATCH] Fix CPU hotplug in networking

The code directly accessed the "cpucontrol" semaphore used
for CPU hotplug. That doesn't work all that well, since the
semaphore doesn't even exist on UP.

include/linux/cpu.h

@@ -37,7 +37,12 @@ extern int register_cpu_notifier(struct notifier_block *nb);
 extern void unregister_cpu_notifier(struct notifier_block *nb);
 
 int cpu_up(unsigned int cpu);
+
+#define lock_cpu_hotplug()	down(&cpucontrol)
+#define unlock_cpu_hotplug()	up(&cpucontrol)
+
 #else
+
 static inline int register_cpu_notifier(struct notifier_block *nb)
 {
 	return 0;
@@ -45,6 +50,10 @@ static inline int register_cpu_notifier(struct notifier_block *nb)
 static inline void unregister_cpu_notifier(struct notifier_block *nb)
 {
 }
+
+#define lock_cpu_hotplug()	do { } while (0)
+#define unlock_cpu_hotplug()		do { } while (0)
+
 #endif /* CONFIG_SMP */
 extern struct sysdev_class cpu_sysdev_class;
 

net/core/flow.c

@@ -286,7 +286,7 @@ void flow_cache_flush(void)
 
 	/* Don't want cpus going down or up during this, also protects
 	 * against multiple callers. */
-	down(&cpucontrol);
+	lock_cpu_hotplug();
 	atomic_set(&info.cpuleft, num_online_cpus());
 	init_completion(&info.completion);
 
@@ -296,7 +296,7 @@ void flow_cache_flush(void)
 	local_bh_enable();
 
 	wait_for_completion(&info.completion);
-	up(&cpucontrol);
+	unlock_cpu_hotplug();
 }
 
 static void __devinit flow_cache_cpu_prepare(int cpu)