Subject: Re: [PATCH nf-next 3/3] netfilter: replace list_head with single linked list

From: Florian Westphal <[email-masked]>
Date: Sat, 9 Jul 2016 01:30:38 +0200

Aaron Conole <[email-masked]> wrote:
> --- a/net/netfilter/core.c
> +++ b/net/netfilter/core
[..]
> +#define nf_entry_dereference(e) \
> +	rcu_dereference_protected(e, lockdep_is_held(&nf_hook_mutex))
>  
> -static struct list_head *nf_find_hook_list(struct net *net,
> -					   const struct nf_hook_ops *reg)
> +static struct nf_hook_entry *nf_find_hook_list(struct net *net,
> +					       const struct nf_hook_ops *reg)
>  {
> -	struct list_head *hook_list = NULL;
> +	struct nf_hook_entry *hook_list = NULL;
>  
>  	if (reg->pf != NFPROTO_NETDEV)
> -		hook_list = &net->nf.hooks[reg->pf][reg->hooknum];
> +		hook_list = rcu_dereference(net->nf.hooks[reg->pf]
> +					    [reg->hooknum]);
>  	else if (reg->hooknum == NF_NETDEV_INGRESS) {
>  #ifdef CONFIG_NETFILTER_INGRESS
>  		if (reg->dev && dev_net(reg->dev) == net)
> -			hook_list = &reg->dev->nf_hooks_ingress;
> +			hook_list =
> +				rcu_dereference(reg->dev->nf_hooks_ingress);

Both of these should use nf_entry_dereference() to avoid the lockdep
splat reported by kbuild robot:

net/netfilter/core.c:75 suspicious rcu_dereference_check() usage!
2 locks held by swapper/1:
#0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff81c2e567>] rtnl_lock+0x17/0x20
#1:  (nf_hook_mutex){+.+...}, at: [<ffffffff81c58fcb>] nf_register_net_hook+0xcb/0x240