linux-kernel - Re: [PATCH 1/2] can: bcm: registration process optimization in bcm_module

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Date:   Fri, 9 Sep 2022 17:04:06 +0200
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     "Ziyang Xuan (William)" <william.xuanziyang@...wei.com>,
        mkl@...gutronix.de, edumazet@...gle.com, kuba@...nel.org,
        linux-can@...r.kernel.org, netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] can: bcm: registration process optimization in
 bcm_module_init()



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