9p/xen: Add cleanup path in p9_trans_xen_init

commit 80a316f upstream.

If xenbus_register_frontend() fails in p9_trans_xen_init,
we should call v9fs_unregister_trans() to do cleanup.

Link: http://lkml.kernel.org/r/20190430143933.19368-1-yuehaibing@huawei.com
Cc: stable@vger.kernel.org
Fixes: 868eb12 ("xen/9pfs: introduce Xen 9pfs transport driver")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/9p/trans_xen.c

@@ -530,13 +530,19 @@ static struct xenbus_driver xen_9pfs_front_driver = {
 
 static int p9_trans_xen_init(void)
 {
+ int rc;
+
  if (!xen_domain())
  return -ENODEV;
 
  pr_info("Initialising Xen transport for 9pfs\n");
 
  v9fs_register_trans(&p9_xen_trans);
- return xenbus_register_frontend(&xen_9pfs_front_driver);
+ rc = xenbus_register_frontend(&xen_9pfs_front_driver);
+ if (rc)
+ v9fs_unregister_trans(&p9_xen_trans);
+
+ return rc;
 }
 module_init(p9_trans_xen_init);