[PATCH net-next v6 09/11] net: sctp: convert sctp_v{4,6}_xmit to use a noref dst when possible

[Marek Mietus <mmietus97@yahoo.com>]

sctp_v{4,6}_xmit unnecessarily clone the dst from the transport when
sending an encapsulated skb.

Reduce this overhead by avoiding the refcount increment introduced by
cloning the dst.

Since t->dst is already assumed to be valid throughout both functions,
it's safe to use the dst without incrementing the refcount.

Signed-off-by: Marek Mietus <mmietus97@yahoo.com>
---
 net/sctp/ipv6.c     | 7 ++++---
 net/sctp/protocol.c | 8 +++++---
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
index 38fd1cf3148f..71fb9ff6276f 100644
--- a/net/sctp/ipv6.c
+++ b/net/sctp/ipv6.c
@@ -219,7 +219,7 @@ int sctp_udp_v6_err(struct sock *sk, struct sk_buff *skb)
 
 static int sctp_v6_xmit(struct sk_buff *skb, struct sctp_transport *t)
 {
-	struct dst_entry *dst = dst_clone(t->dst);
+	struct dst_entry *dst = t->dst;
 	struct flowi6 *fl6 = &t->fl.u.ip6;
 	struct sock *sk = skb->sk;
 	struct ipv6_pinfo *np = inet6_sk(sk);
@@ -243,7 +243,7 @@ static int sctp_v6_xmit(struct sk_buff *skb, struct sctp_transport *t)
 	if (!t->encap_port || !sctp_sk(sk)->udp_port) {
 		int res;
 
-		skb_dst_set(skb, dst);
+		skb_dst_set(skb, dst_clone(dst));
 		rcu_read_lock();
 		res = ip6_xmit(sk, skb, fl6, sk->sk_mark,
 			       rcu_dereference(np->opt),
@@ -261,10 +261,11 @@ static int sctp_v6_xmit(struct sk_buff *skb, struct sctp_transport *t)
 	skb_set_inner_ipproto(skb, IPPROTO_SCTP);
 	label = ip6_make_flowlabel(sock_net(sk), skb, fl6->flowlabel, true, fl6);
 
+	rcu_read_lock();
 	udp_tunnel6_xmit_skb(dst, sk, skb, NULL, &fl6->saddr, &fl6->daddr,
 			     tclass, ip6_dst_hoplimit(dst), label,
 			     sctp_sk(sk)->udp_port, t->encap_port, false, 0);
-	dst_release(dst);
+	rcu_read_unlock();
 	return 0;
 }
 
diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index ff18ed0a65ff..fb26b927391b 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c
@@ -1038,7 +1038,7 @@ static int sctp_inet_supported_addrs(const struct sctp_sock *opt,
 /* Wrapper routine that calls the ip transmit routine. */
 static inline int sctp_v4_xmit(struct sk_buff *skb, struct sctp_transport *t)
 {
-	struct dst_entry *dst = dst_clone(t->dst);
+	struct dst_entry *dst = t->dst;
 	struct flowi4 *fl4 = &t->fl.u.ip4;
 	struct sock *sk = skb->sk;
 	struct inet_sock *inet = inet_sk(sk);
@@ -1056,7 +1056,7 @@ static inline int sctp_v4_xmit(struct sk_buff *skb, struct sctp_transport *t)
 	SCTP_INC_STATS(sock_net(sk), SCTP_MIB_OUTSCTPPACKS);
 
 	if (!t->encap_port || !sctp_sk(sk)->udp_port) {
-		skb_dst_set(skb, dst);
+		skb_dst_set(skb, dst_clone(dst));
 		return __ip_queue_xmit(sk, skb, &t->fl, dscp);
 	}
 
@@ -1070,11 +1070,13 @@ static inline int sctp_v4_xmit(struct sk_buff *skb, struct sctp_transport *t)
 	skb_reset_inner_mac_header(skb);
 	skb_reset_inner_transport_header(skb);
 	skb_set_inner_ipproto(skb, IPPROTO_SCTP);
+
+	rcu_read_lock();
 	udp_tunnel_xmit_skb(dst_rtable(dst), sk, skb, fl4->saddr,
 			    fl4->daddr, dscp, ip4_dst_hoplimit(dst), df,
 			    sctp_sk(sk)->udp_port, t->encap_port, false, false,
 			    0);
-	dst_release(dst);
+	rcu_read_unlock();
 	return 0;
 }
 
-- 
2.51.0