netdev - Re: [PATCH net-next v3] ip_tunnel: Add dst_cache support in lwtunnel

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Date:   Fri, 22 Feb 2019 21:45:09 -0500
From:   David Ahern <dsahern@...il.com>
To:     wenxu@...oud.cn, davem@...emloft.net
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3] ip_tunnel: Add dst_cache support in
 lwtunnel_state of ip tunnel

On 2/22/19 7:32 PM, wenxu@...oud.cn wrote:
> diff --git a/net/core/lwtunnel.c b/net/core/lwtunnel.c
> index 0b17175..f6301af 100644
> --- a/net/core/lwtunnel.c
> +++ b/net/core/lwtunnel.c
> @@ -123,17 +123,18 @@ int lwtunnel_build_state(u16 encap_type,
>  	rcu_read_lock();
>  	ops = rcu_dereference(lwtun_encaps[encap_type]);
>  	if (likely(ops && ops->build_state && try_module_get(ops->owner))) {
> +		rcu_read_unlock();
>  		found = true;
>  		ret = ops->build_state(encap, family, cfg, lws, extack);
>  		if (ret)
>  			module_put(ops->owner);
>  	}
> -	rcu_read_unlock();
>  
>  	/* don't rely on -EOPNOTSUPP to detect match as build_state
>  	 * handlers could return it
>  	 */
>  	if (!found) {
> +		rcu_read_unlock();

I was thinking something much simpler ... like:

rcu_read_lock();

ops = rcu_dereference(lwtun_encaps[encap_type]);
if (likely(ops && ops->build_state && try_module_get(ops->owner))) {
	found = true;

rcu_read_unlock();

if (found) {
	ret = ops->build_state(encap, family, cfg, lws, extack);
	if (ret)
		module_put(ops->owner);
} else {
	NL_SET_ERR_MSG_ATTR(...);
}

>
>  		NL_SET_ERR_MSG_ATTR(extack, encap,
>  				    "LWT encapsulation type not supported");
>  	}
> diff --git a/net/ipv4/ip_tunnel_core.c b/net/ipv4/ip_tunnel_core.c
> index 9a0e67b..334e77a 100644
> --- a/net/ipv4/ip_tunnel_core.c
> +++ b/net/ipv4/ip_tunnel_core.c
> @@ -252,6 +252,14 @@ static int ip_tun_build_state(struct nlattr *attr,
>  
>  	tun_info = lwt_tun_info(new_state);
>  
> +#ifdef CONFIG_DST_CACHE
> +	err = dst_cache_init(&tun_info->dst_cache, GFP_KERNEL);
> +	if (err) {
> +		lwtstate_free(new_state);
> +		return err;
> +	}
> +#endif
> +
>  	if (tb[LWTUNNEL_IP_ID])
>  		tun_info->key.tun_id = nla_get_be64(tb[LWTUNNEL_IP_ID]);
>  
> @@ -278,6 +286,15 @@ static int ip_tun_build_state(struct nlattr *attr,
>  	return 0;
>  }
>  
> +#ifdef CONFIG_DST_CACHE
> +static void ip_tun_destroy_state(struct lwtunnel_state *lwtstate)
> +{
> +	struct ip_tunnel_info *tun_info = lwt_tun_info(lwtstate);
> +
> +	dst_cache_destroy(&tun_info->dst_cache);
> +}> +#endif
> +
>  static int ip_tun_fill_encap_info(struct sk_buff *skb,
>  				  struct lwtunnel_state *lwtstate)
>  {
> @@ -313,6 +330,9 @@ static int ip_tun_cmp_encap(struct lwtunnel_state *a, struct lwtunnel_state *b)
>  
>  static const struct lwtunnel_encap_ops ip_tun_lwt_ops = {
>  	.build_state = ip_tun_build_state,
> +#ifdef CONFIG_DST_CACHE
> +	.destroy_state = ip_tun_destroy_state,
> +#endif

Define ip_tun_destroy_state when DST_CACHE is not enabled so you don't
need this ifdef as well. e.g., move the ifdef around dst_cache_destroy
and its local arg to mirror the init.