[PATCH] Check if cpu can be onlined before calling smp_prepare_cpu()

- Moved check for online cpu out of smp_prepare_cpu()

- Moved default declaration of smp_prepare_cpu() to kernel/cpu.c

- Removed lock_cpu_hotplug() from smp_prepare_cpu() to around it, since
  its called from cpu_up() as well now.

- Removed clearing from cpu_present_map during cpu_offline as it breaks
  using cpu_up() directly during a subsequent online operation.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: "Li, Shaohua" <shaohua.li@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/base/cpu.c

@@ -19,11 +19,6 @@ EXPORT_SYMBOL(cpu_sysdev_class);
 static struct sys_device *cpu_sys_devices[NR_CPUS];
 
 #ifdef CONFIG_HOTPLUG_CPU
-int __attribute__((weak)) smp_prepare_cpu (int cpu)
-{
-	return 0;
-}
-
 static ssize_t show_online(struct sys_device *dev, char *buf)
 {
 	struct cpu *cpu = container_of(dev, struct cpu, sysdev);
@@ -44,9 +39,7 @@ static ssize_t store_online(struct sys_device *dev, const char *buf,
 			kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
 		break;
 	case '1':
-		ret = smp_prepare_cpu(cpu->sysdev.id);
-		if (!ret)
-			ret = cpu_up(cpu->sysdev.id);
+		ret = cpu_up(cpu->sysdev.id);
 		if (!ret)
 			kobject_uevent(&dev->kobj, KOBJ_ONLINE);
 		break;