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

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Date:   Thu, 8 Sep 2022 09:10:15 +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()



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)