xen, cpu_hotplug: call device_offline instead of cpu_down

When offlining a cpu, instead of cpu_down, call device_offline, which
also takes care of updating the cpu.dev.offline field. This keeps the
sysfs file /sys/devices/system/cpu/cpuN/online, up to date.  Also move
the call to disable_hotplug_cpu, because it makes more sense to have it
there.

We don't call device_online at cpu-hotplug time, because that would
immediately take the cpu online, while we want to retain the current
behaviour: the user needs to explicitly enable the cpu after it has
been hotplugged.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
CC: konrad.wilk@oracle.com
CC: boris.ostrovsky@oracle.com
CC: david.vrabel@citrix.com

drivers/xen/cpu_hotplug.c

@@ -18,6 +18,11 @@ static void enable_hotplug_cpu(int cpu)
 
 static void disable_hotplug_cpu(int cpu)
 {
+	if (cpu_online(cpu)) {
+		lock_device_hotplug();
+		device_offline(get_cpu_device(cpu));
+		unlock_device_hotplug();
+	}
 	if (cpu_present(cpu))
 		xen_arch_unregister_cpu(cpu);
 
@@ -55,7 +60,6 @@ static void vcpu_hotplug(unsigned int cpu)
 		enable_hotplug_cpu(cpu);
 		break;
 	case 0:
-		(void)cpu_down(cpu);
 		disable_hotplug_cpu(cpu);
 		break;
 	default: