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

[Ziyang Xuan (William)]

> 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;
> }
> 

I had a simple test with can_raw. kernel modification as following:

--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -118,6 +118,8 @@ static int can_create(struct net *net, struct socket *sock, int protocol,
        const struct can_proto *cp;
        int err = 0;

+       printk("%s: protocol: %d\n", __func__, protocol);
+
        sock->state = SS_UNCONNECTED;

        if (protocol < 0 || protocol >= CAN_NPROTO)
diff --git a/net/can/raw.c b/net/can/raw.c
index 5dca1e9e44cf..6052fd0cc7b2 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -943,6 +943,9 @@ static __init int raw_module_init(void)
        pr_info("can: raw protocol\n");

        err = can_proto_register(&raw_can_proto);
+       printk("%s: can_proto_register done\n", __func__);
+       msleep(5000); // 5s
+       printk("%s: to register_netdevice_notifier\n", __func__);
        if (err < 0)
                pr_err("can: registration of raw protocol failed\n");
        else

I added 5 seconds delay after can_proto_register() and some debugs.
Testcase codes just try to create a CAN_RAW socket in user space as following:

int main(int argc, char **argv)
{
        int s;

        s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
        if (s < 0) {
                perror("socket");
                return 0;
        }
        close(s);
        return 0;
}

Execute 'modprobe can_raw' and the testcase we can get message as following:

[  109.312767] can: raw protocol
[  109.312772] raw_module_init: can_proto_register done
[  111.296178] can_create: protocol: 1
[  114.809141] raw_module_init: to register_netdevice_notifier

It proved that it can create CAN_RAW socket and process socket once can_proto_register() successfully.
CAN_BCM is the same.

In the vast majority of cases, creating protocol socket and operating it are after protocol module initialization.
The scenario that I pointed in my patch is a low probability.

af_packet.c and af_key.c do like that doesn't mean it's very correct. I think so.

Thank you for your prompt reply.

> 
> 
> 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@xxxxxxxxxx>
>>> ---
>>>   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@xxxxxxxxxx/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)
> .