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

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Date:   Mon, 12 Sep 2022 16:54:48 +0200
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     "Ziyang Xuan (William)" <william.xuanziyang@...wei.com>,
        edumazet@...gle.com, kuba@...nel.org, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] can: bcm: registration process optimization in
 bcm_module_init()



On 12.09.22 14:00, Marc Kleine-Budde wrote:
> On 09.09.2022 17:04:06, Oliver Hartkopp wrote:
>>
>>
>> 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.
> 
> The notifier calls bcm_notifier() first, which will loop over the
> bcm_notifier_list. The list is empty if there are no sockets open, yet.
> So from my point of view this change looks fine.
> 
> IMHO it's better to make a series where all these notifiers are moved in
> front of the respective socket proto_register().

Notifiers and/or pernet_subsys ?

But yes, that would be better to have a clean consistent sequence in all 
these cases.

Would this affect af_packet.c then too?

Regards,
Oliver