rtnetlink: Use register_pernet_subsys() in rtnl_net_debug_init().

rtnl_net_debug_init() registers rtnl_net_debug_net_ops by
register_pernet_device() but calls unregister_pernet_subsys()
in case register_netdevice_notifier() fails.

It corrupts pernet_list because first_device is updated in
register_pernet_device() but not unregister_pernet_subsys().

Let's fix it by calling register_pernet_subsys() instead.

The _subsys() one fits better for the use case because it keeps
the notifier alive until default_device_exit_net(), giving it
more chance to test NETDEV_UNREGISTER.

Fixes: 03fa534 ("rtnetlink: Add ASSERT_RTNL_NET() placeholder for netdev notifier.")
Signed-off-by: Kuniyuki Iwashima <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: q2ven

net/core/rtnl_net_debug.c

@@ -102,7 +102,7 @@ static int __init rtnl_net_debug_init(void)
 {
 	int ret;
 
-	ret = register_pernet_device(&rtnl_net_debug_net_ops);
+	ret = register_pernet_subsys(&rtnl_net_debug_net_ops);
 	if (ret)
 		return ret;