Re: [PATCH 1/2] can: bcm: registration process optimization in bcm_module_init()

From: Oliver Hartkopp
Date: Fri Sep 09 2022 - 11:04:23 EST




On 09.09.22 05:58, Ziyang Xuan (William) wrote:


On 9/8/22 13:14, Ziyang Xuan (William) wrote:
Just another reference which make it clear that the reordering of function calls in your patch is likely not correct:

https://elixir.bootlin.com/linux/v5.19.7/source/net/packet/af_packet.c#L4734

static int __init packet_init(void)
{
         int rc;

         rc = proto_register(&packet_proto, 0);
         if (rc)
                 goto out;
         rc = sock_register(&packet_family_ops);
         if (rc)
                 goto out_proto;
         rc = register_pernet_subsys(&packet_net_ops);
         if (rc)
                 goto out_sock;
         rc = register_netdevice_notifier(&packet_netdev_notifier);
         if (rc)
                 goto out_pernet;

         return 0;

out_pernet:
         unregister_pernet_subsys(&packet_net_ops);
out_sock:
         sock_unregister(PF_PACKET);
out_proto:
         proto_unregister(&packet_proto);
out:
         return rc;
}


Yes,all these socket operations need time, most likely, register_netdevice_notifier() and register_pernet_subsys() had been done.
But it maybe not for some reasons, for example, cpu# that runs {raw,bcm}_module_init() is stuck temporary,
or pernet_ops_rwsem lock competition in register_netdevice_notifier() and register_pernet_subsys().

If the condition which I pointed happens, I think my solution can solve.


No, I don't think so.

We need to maintain the exact order which is depicted in the af_packet.c code from above as the notifier call references the sock pointer.

Regards,
Oliver