Bluetooth: Fix error handling for l2cap_init()

create_singlethread_workqueue() may fail with errors such as -ENOMEM. If
this happens, the return value is not set to a negative value and the
module load will succeed. It will then crash on module unload because of
a destroy_workqueue() call on a NULL pointer.

Additionally, the _busy_wq workqueue is not being destroyed if any
errors happen on l2cap_init().
Signed-off-by: Anderson Lizardo <anderson.lizardo@openbossa.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

net/bluetooth/l2cap.c

@@ -4871,8 +4871,10 @@ static int __init l2cap_init(void)
 		return err;
 
 	_busy_wq = create_singlethread_workqueue("l2cap");
-	if (!_busy_wq)
-		goto error;
+	if (!_busy_wq) {
+		proto_unregister(&l2cap_proto);
+		return -ENOMEM;
+	}
 
 	err = bt_sock_register(BTPROTO_L2CAP, &l2cap_sock_family_ops);
 	if (err < 0) {
@@ -4900,6 +4902,7 @@ static int __init l2cap_init(void)
 	return 0;
 
 error:
+	destroy_workqueue(_busy_wq);
 	proto_unregister(&l2cap_proto);
 	return err;
 }