xenbus: remove transaction holder from list before freeing

After allocation the item is being placed on the list right away.
Consequently it needs to be taken off the list before freeing in the
case xenbus_dev_request_and_reply() failed, as in that case the
callback (xenbus_dev_queue_reply()) is not being called (and if it
was called, it should do both).

Fixes: 5584ea2
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

drivers/xen/xenbus/xenbus_dev_frontend.c

@@ -442,8 +442,10 @@ static int xenbus_write_transaction(unsigned msg_type,
 		return xenbus_command_reply(u, XS_ERROR, "ENOENT");
 
 	rc = xenbus_dev_request_and_reply(&u->u.msg, u);
-	if (rc)
+	if (rc && trans) {
+		list_del(&trans->list);
 		kfree(trans);
+	}
 
 out:
 	return rc;