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>

diff --git a/drivers/usb/atm/usbatm.c b/drivers/usb/atm/usbatm.c
index 309073f..ab091fa 100644
--- a/drivers/usb/atm/usbatm.c
+++ b/drivers/usb/atm/usbatm.c
@@ -1001,6 +1001,7 @@
 
 	daemonize(instance->driver->driver_name);
 	allow_signal(SIGTERM);
+	instance->thread_pid = get_current()->pid;
 
 	complete(&instance->thread_started);
 
@@ -1025,10 +1026,6 @@
 		return ret;
 	}
 
-	mutex_lock(&instance->serialize);
-	instance->thread_pid = ret;
-	mutex_unlock(&instance->serialize);
-
 	wait_for_completion(&instance->thread_started);
 
 	return 0;