use lock_device_hotplug before checking cpu masks

 drivers/xen/cpu_hotplug.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/xen/cpu_hotplug.c b/drivers/xen/cpu_hotplug.c
index 5676aef..43ef131 100644
--- a/drivers/xen/cpu_hotplug.c
+++ b/drivers/xen/cpu_hotplug.c
@@ -10,19 +10,20 @@

 static void enable_hotplug_cpu(int cpu)
 {
+       lock_device_hotplug();
        if (!cpu_present(cpu))
                xen_arch_register_cpu(cpu);
+       unlock_device_hotplug();

        set_cpu_present(cpu, true);
 }

 static void disable_hotplug_cpu(int cpu)
 {
-       if (cpu_online(cpu)) {
-               lock_device_hotplug();
+       lock_device_hotplug();
+       if (cpu_online(cpu))
                device_offline(get_cpu_device(cpu));
-               unlock_device_hotplug();
-       }
+       unlock_device_hotplug();
        if (cpu_present(cpu))
                xen_arch_unregister_cpu(cpu);