tcp: add tcp_inet6_sk() helper

TCP ipv6 fast path dereferences a pointer to get to the inet6
part of a tcp socket, but given the fixed memory placement,
we can do better and avoid a possible cache line miss.

This also reduces register pressure, since we let the compiler
know about this memory placement.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/tcp_ipv6.c

@@ -90,6 +90,17 @@ static struct tcp_md5sig_key *tcp_v6_md5_do_lookup(const struct sock *sk,
 }
 #endif
 
+/* Helper returning the inet6 address from a given tcp socket.
+ * It can be used in TCP stack instead of inet6_sk(sk).
+ * This avoids a dereference and allow compiler optimizations.
+ */
+static struct ipv6_pinfo *tcp_inet6_sk(const struct sock *sk)
+{
+	struct tcp6_sock *tcp6 = container_of(tcp_sk(sk), struct tcp6_sock, tcp);
+
+	return &tcp6->inet6;
+}
+
 static void inet6_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb)
 {
 	struct dst_entry *dst = skb_dst(skb);
@@ -99,7 +110,7 @@ static void inet6_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb)
 
 		sk->sk_rx_dst = dst;
 		inet_sk(sk)->rx_dst_ifindex = skb->skb_iif;
-		inet6_sk(sk)->rx_dst_cookie = rt6_get_cookie(rt);
+		tcp_inet6_sk(sk)->rx_dst_cookie = rt6_get_cookie(rt);
 	}
 }
 
@@ -138,7 +149,7 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 	struct sockaddr_in6 *usin = (struct sockaddr_in6 *) uaddr;
 	struct inet_sock *inet = inet_sk(sk);
 	struct inet_connection_sock *icsk = inet_csk(sk);
-	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct ipv6_pinfo *np = tcp_inet6_sk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct in6_addr *saddr = NULL, *final_p, final;
 	struct ipv6_txoptions *opt;
@@ -390,7 +401,7 @@ static int tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 	if (sk->sk_state == TCP_CLOSE)
 		goto out;
 
-	if (ipv6_hdr(skb)->hop_limit < inet6_sk(sk)->min_hopcount) {
+	if (ipv6_hdr(skb)->hop_limit < tcp_inet6_sk(sk)->min_hopcount) {
 		__NET_INC_STATS(net, LINUX_MIB_TCPMINTTLDROP);
 		goto out;
 	}
@@ -405,7 +416,7 @@ static int tcp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 		goto out;
 	}
 
-	np = inet6_sk(sk);
+	np = tcp_inet6_sk(sk);
 
 	if (type == NDISC_REDIRECT) {
 		if (!sock_owned_by_user(sk)) {
@@ -478,7 +489,7 @@ static int tcp_v6_send_synack(const struct sock *sk, struct dst_entry *dst,
 			      enum tcp_synack_type synack_type)
 {
 	struct inet_request_sock *ireq = inet_rsk(req);
-	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct ipv6_pinfo *np = tcp_inet6_sk(sk);
 	struct ipv6_txoptions *opt;
 	struct flowi6 *fl6 = &fl->u.ip6;
 	struct sk_buff *skb;
@@ -737,7 +748,7 @@ static void tcp_v6_init_req(struct request_sock *req,
 {
 	bool l3_slave = ipv6_l3mdev_skb(TCP_SKB_CB(skb)->header.h6.flags);
 	struct inet_request_sock *ireq = inet_rsk(req);
-	const struct ipv6_pinfo *np = inet6_sk(sk_listener);
+	const struct ipv6_pinfo *np = tcp_inet6_sk(sk_listener);
 
 	ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
 	ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
@@ -1066,9 +1077,8 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
 {
 	struct inet_request_sock *ireq;
 	struct ipv6_pinfo *newnp;
-	const struct ipv6_pinfo *np = inet6_sk(sk);
+	const struct ipv6_pinfo *np = tcp_inet6_sk(sk);
 	struct ipv6_txoptions *opt;
-	struct tcp6_sock *newtcp6sk;
 	struct inet_sock *newinet;
 	struct tcp_sock *newtp;
 	struct sock *newsk;
@@ -1088,11 +1098,10 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
 		if (!newsk)
 			return NULL;
 
-		newtcp6sk = (struct tcp6_sock *)newsk;
-		inet_sk(newsk)->pinet6 = &newtcp6sk->inet6;
+		inet_sk(newsk)->pinet6 = tcp_inet6_sk(newsk);
 
 		newinet = inet_sk(newsk);
-		newnp = inet6_sk(newsk);
+		newnp = tcp_inet6_sk(newsk);
 		newtp = tcp_sk(newsk);
 
 		memcpy(newnp, np, sizeof(struct ipv6_pinfo));
@@ -1156,12 +1165,11 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
 	ip6_dst_store(newsk, dst, NULL, NULL);
 	inet6_sk_rx_dst_set(newsk, skb);
 
-	newtcp6sk = (struct tcp6_sock *)newsk;
-	inet_sk(newsk)->pinet6 = &newtcp6sk->inet6;
+	inet_sk(newsk)->pinet6 = tcp_inet6_sk(newsk);
 
 	newtp = tcp_sk(newsk);
 	newinet = inet_sk(newsk);
-	newnp = inet6_sk(newsk);
+	newnp = tcp_inet6_sk(newsk);
 
 	memcpy(newnp, np, sizeof(struct ipv6_pinfo));
 
@@ -1276,9 +1284,9 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
  */
 static int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
 {
-	struct ipv6_pinfo *np = inet6_sk(sk);
-	struct tcp_sock *tp;
+	struct ipv6_pinfo *np = tcp_inet6_sk(sk);
 	struct sk_buff *opt_skb = NULL;
+	struct tcp_sock *tp;
 
 	/* Imagine: socket is IPv6. IPv4 packet arrives,
 	   goes to IPv4 receive handler and backlogged.
@@ -1524,7 +1532,7 @@ static int tcp_v6_rcv(struct sk_buff *skb)
 			return 0;
 		}
 	}
-	if (hdr->hop_limit < inet6_sk(sk)->min_hopcount) {
+	if (hdr->hop_limit < tcp_inet6_sk(sk)->min_hopcount) {
 		__NET_INC_STATS(net, LINUX_MIB_TCPMINTTLDROP);
 		goto discard_and_relse;
 	}
@@ -1669,7 +1677,7 @@ static void tcp_v6_early_demux(struct sk_buff *skb)
 			struct dst_entry *dst = READ_ONCE(sk->sk_rx_dst);
 
 			if (dst)
-				dst = dst_check(dst, inet6_sk(sk)->rx_dst_cookie);
+				dst = dst_check(dst, tcp_inet6_sk(sk)->rx_dst_cookie);
 			if (dst &&
 			    inet_sk(sk)->rx_dst_ifindex == skb->skb_iif)
 				skb_dst_set_noref(skb, dst);