lwtunnel: Add destroy state operation

Users of lwt tunnels may set up some secondary state in build_state
function. Add a corresponding destroy_state function to allow users to
clean up state. This destroy state function is called from lwstate_free.
Also, we now free lwstate using kfree_rcu so user can assume structure
is not freed before rcu.

Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/lwtunnel.h

@@ -29,13 +29,15 @@ struct lwtunnel_state {
 	int		(*orig_input)(struct sk_buff *);
 	int             len;
 	__u16		headroom;
+	struct		rcu_head rcu;
 	__u8            data[0];
 };
 
 struct lwtunnel_encap_ops {
 	int (*build_state)(struct net_device *dev, struct nlattr *encap,
 			   unsigned int family, const void *cfg,
 			   struct lwtunnel_state **ts);
+	void (*destroy_state)(struct lwtunnel_state *lws);
 	int (*output)(struct net *net, struct sock *sk, struct sk_buff *skb);
 	int (*input)(struct sk_buff *skb);
 	int (*fill_encap)(struct sk_buff *skb,
@@ -46,10 +48,7 @@ struct lwtunnel_encap_ops {
 };
 
 #ifdef CONFIG_LWTUNNEL
-static inline void lwtstate_free(struct lwtunnel_state *lws)
-{
-	kfree(lws);
-}
+void lwtstate_free(struct lwtunnel_state *lws);
 
 static inline struct lwtunnel_state *
 lwtstate_get(struct lwtunnel_state *lws)

net/core/lwtunnel.c

@@ -130,6 +130,19 @@ int lwtunnel_build_state(struct net_device *dev, u16 encap_type,
 }
 EXPORT_SYMBOL(lwtunnel_build_state);
 
+void lwtstate_free(struct lwtunnel_state *lws)
+{
+	const struct lwtunnel_encap_ops *ops = lwtun_encaps[lws->type];
+
+	if (ops->destroy_state) {
+		ops->destroy_state(lws);
+		kfree_rcu(lws, rcu);
+	} else {
+		kfree(lws);
+	}
+}
+EXPORT_SYMBOL(lwtstate_free);
+
 int lwtunnel_fill_encap(struct sk_buff *skb, struct lwtunnel_state *lwtstate)
 {
 	const struct lwtunnel_encap_ops *ops;