usbatm: fix tiny race

If usbatm_do_heavy_init finishes before usbatm_heavy_init
writes the pid, the disconnect method could shoot down the
wrong process if the pid has been recycled.
Signed-off-by: Duncan Sands <baldrick@free.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/atm/usbatm.c

@@ -1001,6 +1001,7 @@ static int usbatm_do_heavy_init(void *arg)
 
 	daemonize(instance->driver->driver_name);
 	allow_signal(SIGTERM);
+	instance->thread_pid = get_current()->pid;
 
 	complete(&instance->thread_started);
 
@@ -1025,10 +1026,6 @@ static int usbatm_heavy_init(struct usbatm_data *instance)
 		return ret;
 	}
 
-	mutex_lock(&instance->serialize);
-	instance->thread_pid = ret;
-	mutex_unlock(&instance->serialize);
-
 	wait_for_completion(&instance->thread_started);
 
 	return 0;