On Fri, Jul 17, 2026 at 02:55:54PM +0800, 何敏红 wrote:

 

Hi Andrew,

Thanks for the review.

quoted

Think about what happens when phonet_netlink_register() fails.

I checked that path. By the time phonet_netlink_register() runs,
pernet, the proc entry and the netdevice notifier have all been
registered successfully. On failure, rtnl_register_many() already
unwinds any partially registered handlers, and phonet_device_exit()
then tears down the notifier/pernet/proc that were set up. So this is
not the same issue as calling unregister_netdevice_notifier() for a
notifier that never got registered.

int __init phonet_device_init(void)
{
        int err = register_pernet_subsys(&phonet_net_ops);
        if (err)
                return err;

        proc_create_net("pnresource", 0, init_net.proc_net, &pn_res_seq_ops,
                        sizeof(struct seq_net_private));
        register_netdevice_notifier(&phonet_device_notifier);
        err = phonet_netlink_register();
        if (err)
                phonet_device_exit();

If we get here, phonet_netlink_register() failed.

What exactly does phonet_netlink_register() do:

int __init phonet_netlink_register(void)
{
	return rtnl_register_many(phonet_rtnl_msg_handlers);
}

And what does phonet_device_exit() do?

void phonet_device_exit(void)
{
        rtnl_unregister_all(PF_PHONET);
        unregister_netdevice_notifier(&phonet_device_notifier);
        unregister_pernet_subsys(&phonet_net_ops);
        remove_proc_entry("pnresource", init_net.proc_net);
}

So it tries to unregister something which was not registered. That is
generally a bad idea.

The general pattern in the Linux kernel is that on error, you
carefully unwind everything which succeeded so far. Often you do that
at the end, with a series of goto statements and labels.

Calling the "mirror" function on error does not work, since that
function assumes everything went correctly in its peer.

	Andrew