tunnels: add __rcu annotations

Add __rcu annotations to :
(struct ip_tunnel)->prl
(struct ip_tunnel_prl_entry)->next
(struct xfrm_tunnel)->next
struct xfrm_tunnel *tunnel4_handlers
struct xfrm_tunnel *tunnel64_handlers

And use appropriate rcu primitives to reduce sparse warnings if
CONFIG_SPARSE_RCU_POINTER=y

Signed-off-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/ipip.h

···
 #ifdef CONFIG_IPV6_SIT_6RD
 	struct ip_tunnel_6rd_parm	ip6rd;
 #endif
-	struct ip_tunnel_prl_entry	*prl;		/* potential router list */
+	struct ip_tunnel_prl_entry __rcu *prl;		/* potential router list */
 	unsigned int			prl_count;	/* # of entries in PRL */
 };
 
 struct ip_tunnel_prl_entry {
-	struct ip_tunnel_prl_entry	*next;
+	struct ip_tunnel_prl_entry __rcu *next;
 	__be32				addr;
 	u16				flags;
 	struct rcu_head			rcu_head;

include/net/xfrm.h

···
 	int (*handler)(struct sk_buff *skb);
 	int (*err_handler)(struct sk_buff *skb, u32 info);
 
-	struct xfrm_tunnel *next;
+	struct xfrm_tunnel __rcu *next;
 	int priority;
 };
 

net/ipv4/tunnel4.c

···
 #include <net/protocol.h>
 #include <net/xfrm.h>
 
-static struct xfrm_tunnel *tunnel4_handlers __read_mostly;
-static struct xfrm_tunnel *tunnel64_handlers __read_mostly;
+static struct xfrm_tunnel __rcu *tunnel4_handlers __read_mostly;
+static struct xfrm_tunnel __rcu *tunnel64_handlers __read_mostly;
 static DEFINE_MUTEX(tunnel4_mutex);
 
-static inline struct xfrm_tunnel **fam_handlers(unsigned short family)
+static inline struct xfrm_tunnel __rcu **fam_handlers(unsigned short family)
 {
 	return (family == AF_INET) ? &tunnel4_handlers : &tunnel64_handlers;
 }
 
 int xfrm4_tunnel_register(struct xfrm_tunnel *handler, unsigned short family)
 {
-	struct xfrm_tunnel **pprev;
+	struct xfrm_tunnel __rcu **pprev;
+	struct xfrm_tunnel *t;
+
 	int ret = -EEXIST;
 	int priority = handler->priority;
 
 	mutex_lock(&tunnel4_mutex);
 
-	for (pprev = fam_handlers(family); *pprev; pprev = &(*pprev)->next) {
-		if ((*pprev)->priority > priority)
+	for (pprev = fam_handlers(family);
+	     (t = rcu_dereference_protected(*pprev,
+			lockdep_is_held(&tunnel4_mutex))) != NULL;
+	     pprev = &t->next) {
+		if (t->priority > priority)
 			break;
-		if ((*pprev)->priority == priority)
+		if (t->priority == priority)
 			goto err;
 	}
 
···
 
 int xfrm4_tunnel_deregister(struct xfrm_tunnel *handler, unsigned short family)
 {
-	struct xfrm_tunnel **pprev;
+	struct xfrm_tunnel __rcu **pprev;
+	struct xfrm_tunnel *t;
 	int ret = -ENOENT;
 
 	mutex_lock(&tunnel4_mutex);
 
-	for (pprev = fam_handlers(family); *pprev; pprev = &(*pprev)->next) {
-		if (*pprev == handler) {
+	for (pprev = fam_handlers(family);
+	     (t = rcu_dereference_protected(*pprev,
+			lockdep_is_held(&tunnel4_mutex))) != NULL;
+	     pprev = &t->next) {
+		if (t == handler) {
 			*pprev = handler->next;
 			ret = 0;
 			break;