nfnetlink: add nfnl_dereference_protected helper

to avoid overly long line in followup patch.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nfnetlink.c

@@ -33,6 +33,10 @@ MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
 MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NETFILTER);
 
+#define nfnl_dereference_protected(id) \
+	rcu_dereference_protected(table[(id)].subsys, \
+				  lockdep_nfnl_is_held((id)))
+
 static char __initdata nfversion[] = "0.30";
 
 static struct {
@@ -208,8 +212,7 @@ static int nfnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 		} else {
 			rcu_read_unlock();
 			nfnl_lock(subsys_id);
-			if (rcu_dereference_protected(table[subsys_id].subsys,
-				lockdep_is_held(&table[subsys_id].mutex)) != ss ||
+			if (nfnl_dereference_protected(subsys_id) != ss ||
 			    nfnetlink_find_client(type, ss) != nc)
 				err = -EAGAIN;
 			else if (nc->call)
@@ -299,15 +302,13 @@ static void nfnetlink_rcv_batch(struct sk_buff *skb, struct nlmsghdr *nlh,
 	skb->sk = oskb->sk;
 
 	nfnl_lock(subsys_id);
-	ss = rcu_dereference_protected(table[subsys_id].subsys,
-				       lockdep_is_held(&table[subsys_id].mutex));
+	ss = nfnl_dereference_protected(subsys_id);
 	if (!ss) {
 #ifdef CONFIG_MODULES
 		nfnl_unlock(subsys_id);
 		request_module("nfnetlink-subsys-%d", subsys_id);
 		nfnl_lock(subsys_id);
-		ss = rcu_dereference_protected(table[subsys_id].subsys,
-					       lockdep_is_held(&table[subsys_id].mutex));
+		ss = nfnl_dereference_protected(subsys_id);
 		if (!ss)
 #endif
 		{