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

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Date:   Thu, 8 Sep 2022 09:17:43 +0200
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Ziyang Xuan <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()

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;
}



On 08.09.22 09:10, Oliver Hartkopp wrote:
> 
> 
> On 08.09.22 05:04, Ziyang Xuan wrote:
>> Now, register_netdevice_notifier() and register_pernet_subsys() are both
>> after can_proto_register(). It can create CAN_BCM socket and process 
>> socket
>> once can_proto_register() successfully, so it is possible missing 
>> notifier
>> event or proc node creation because notifier or bcm proc directory is not
>> registered or created yet. Although this is a low probability 
>> scenario, it
>> is not impossible.
>>
>> Move register_pernet_subsys() and register_netdevice_notifier() to the
>> front of can_proto_register(). In addition, register_pernet_subsys() and
>> register_netdevice_notifier() may fail, check their results are 
>> necessary.
>>
>> Signed-off-by: Ziyang Xuan <william.xuanziyang@...wei.com>
>> ---
>>   net/can/bcm.c | 18 +++++++++++++++---
>>   1 file changed, 15 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/can/bcm.c b/net/can/bcm.c
>> index e60161bec850..e2783156bfd1 100644
>> --- a/net/can/bcm.c
>> +++ b/net/can/bcm.c
>> @@ -1744,15 +1744,27 @@ static int __init bcm_module_init(void)
>>       pr_info("can: broadcast manager protocol\n");
>> +    err = register_pernet_subsys(&canbcm_pernet_ops);
>> +    if (err)
>> +        return err;
> 
> Analogue to your patch for the CAN_RAW socket here (which has been 
> applied to can-next right now) ...
> 
> https://lore.kernel.org/linux-can/7af9401f0d2d9fed36c1667b5ac9b8df8f8b87ee.1661584485.git.william.xuanziyang@huawei.com/T/#u 
> 
> 
> ... I'm not sure whether this is the right sequence to acquire the 
> different resources here.
> 
> E.g. in ipsec_pfkey_init() in af_key.c
> 
> https://elixir.bootlin.com/linux/v5.19.7/source/net/key/af_key.c#L3887
> 
> proto_register() is executed before register_pernet_subsys()
> 
> Which seems to be more natural to me.
> 
> Best regards,
> Oliver
> 
>> +
>> +    err = register_netdevice_notifier(&canbcm_notifier);
>> +    if (err)
>> +        goto register_notifier_failed;
>> +
>>       err = can_proto_register(&bcm_can_proto);
>>       if (err < 0) {
>>           printk(KERN_ERR "can: registration of bcm protocol failed\n");
>> -        return err;
>> +        goto register_proto_failed;
>>       }
>> -    register_pernet_subsys(&canbcm_pernet_ops);
>> -    register_netdevice_notifier(&canbcm_notifier);
>>       return 0;
>> +
>> +register_proto_failed:
>> +    unregister_netdevice_notifier(&canbcm_notifier);
>> +register_notifier_failed:
>> +    unregister_pernet_subsys(&canbcm_pernet_ops);
>> +    return err;
>>   }
>>   static void __exit bcm_module_exit(void)