udp6: don't make extra copies of iflow

udpv6_sendmsg() first initialises an on-stack 88B struct flowi6 and then
copies it into cork, which is expensive. Avoid the copy in corkless case
by initialising on-stack cork->fl directly.

The main part is a couple of lines under !corkreq check. The rest
converts fl6 variable to be a pointer.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Reviewed-by: NWillem de Bruijn <willemb@google.com>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>

net/ipv6/udp.c

@@ -1294,7 +1294,8 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	struct ipv6_txoptions *opt = NULL;
 	struct ipv6_txoptions *opt_to_free = NULL;
 	struct ip6_flowlabel *flowlabel = NULL;
-	struct flowi6 fl6;
+	struct inet_cork_full cork;
+	struct flowi6 *fl6 = &cork.fl.u.ip6;
 	struct dst_entry *dst;
 	struct ipcm6_cookie ipc6;
 	int addr_len = msg->msg_namelen;
@@ -1384,19 +1385,19 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	}
 	ulen += sizeof(struct udphdr);
 
-	memset(&fl6, 0, sizeof(fl6));
+	memset(fl6, 0, sizeof(*fl6));
 
 	if (sin6) {
 		if (sin6->sin6_port == 0)
 			return -EINVAL;
 
-		fl6.fl6_dport = sin6->sin6_port;
+		fl6->fl6_dport = sin6->sin6_port;
 		daddr = &sin6->sin6_addr;
 
 		if (np->sndflow) {
-			fl6.flowlabel = sin6->sin6_flowinfo&IPV6_FLOWINFO_MASK;
-			if (fl6.flowlabel&IPV6_FLOWLABEL_MASK) {
-				flowlabel = fl6_sock_lookup(sk, fl6.flowlabel);
+			fl6->flowlabel = sin6->sin6_flowinfo&IPV6_FLOWINFO_MASK;
+			if (fl6->flowlabel & IPV6_FLOWLABEL_MASK) {
+				flowlabel = fl6_sock_lookup(sk, fl6->flowlabel);
 				if (IS_ERR(flowlabel))
 					return -EINVAL;
 			}
@@ -1413,24 +1414,24 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		if (addr_len >= sizeof(struct sockaddr_in6) &&
 		    sin6->sin6_scope_id &&
 		    __ipv6_addr_needs_scope_id(__ipv6_addr_type(daddr)))
-			fl6.flowi6_oif = sin6->sin6_scope_id;
+			fl6->flowi6_oif = sin6->sin6_scope_id;
 	} else {
 		if (sk->sk_state != TCP_ESTABLISHED)
 			return -EDESTADDRREQ;
 
-		fl6.fl6_dport = inet->inet_dport;
+		fl6->fl6_dport = inet->inet_dport;
 		daddr = &sk->sk_v6_daddr;
-		fl6.flowlabel = np->flow_label;
+		fl6->flowlabel = np->flow_label;
 		connected = true;
 	}
 
-	if (!fl6.flowi6_oif)
-		fl6.flowi6_oif = sk->sk_bound_dev_if;
+	if (!fl6->flowi6_oif)
+		fl6->flowi6_oif = sk->sk_bound_dev_if;
 
-	if (!fl6.flowi6_oif)
-		fl6.flowi6_oif = np->sticky_pktinfo.ipi6_ifindex;
+	if (!fl6->flowi6_oif)
+		fl6->flowi6_oif = np->sticky_pktinfo.ipi6_ifindex;
 
-	fl6.flowi6_uid = sk->sk_uid;
+	fl6->flowi6_uid = sk->sk_uid;
 
 	if (msg->msg_controllen) {
 		opt = &opt_space;
@@ -1440,14 +1441,14 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 
 		err = udp_cmsg_send(sk, msg, &ipc6.gso_size);
 		if (err > 0)
-			err = ip6_datagram_send_ctl(sock_net(sk), sk, msg, &fl6,
+			err = ip6_datagram_send_ctl(sock_net(sk), sk, msg, fl6,
 						    &ipc6);
 		if (err < 0) {
 			fl6_sock_release(flowlabel);
 			return err;
 		}
-		if ((fl6.flowlabel&IPV6_FLOWLABEL_MASK) && !flowlabel) {
-			flowlabel = fl6_sock_lookup(sk, fl6.flowlabel);
+		if ((fl6->flowlabel&IPV6_FLOWLABEL_MASK) && !flowlabel) {
+			flowlabel = fl6_sock_lookup(sk, fl6->flowlabel);
 			if (IS_ERR(flowlabel))
 				return -EINVAL;
 		}
@@ -1464,16 +1465,17 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	opt = ipv6_fixup_options(&opt_space, opt);
 	ipc6.opt = opt;
 
-	fl6.flowi6_proto = sk->sk_protocol;
-	fl6.flowi6_mark = ipc6.sockc.mark;
-	fl6.daddr = *daddr;
-	if (ipv6_addr_any(&fl6.saddr) && !ipv6_addr_any(&np->saddr))
-		fl6.saddr = np->saddr;
-	fl6.fl6_sport = inet->inet_sport;
+	fl6->flowi6_proto = sk->sk_protocol;
+	fl6->flowi6_mark = ipc6.sockc.mark;
+	fl6->daddr = *daddr;
+	if (ipv6_addr_any(&fl6->saddr) && !ipv6_addr_any(&np->saddr))
+		fl6->saddr = np->saddr;
+	fl6->fl6_sport = inet->inet_sport;
 
 	if (cgroup_bpf_enabled(CGROUP_UDP6_SENDMSG) && !connected) {
 		err = BPF_CGROUP_RUN_PROG_UDP6_SENDMSG_LOCK(sk,
-					   (struct sockaddr *)sin6, &fl6.saddr);
+					   (struct sockaddr *)sin6,
+					   &fl6->saddr);
 		if (err)
 			goto out_no_dst;
 		if (sin6) {
@@ -1489,32 +1491,32 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 				err = -EINVAL;
 				goto out_no_dst;
 			}
-			fl6.fl6_dport = sin6->sin6_port;
-			fl6.daddr = sin6->sin6_addr;
+			fl6->fl6_dport = sin6->sin6_port;
+			fl6->daddr = sin6->sin6_addr;
 		}
 	}
 
-	if (ipv6_addr_any(&fl6.daddr))
-		fl6.daddr.s6_addr[15] = 0x1; /* :: means loopback (BSD'ism) */
+	if (ipv6_addr_any(&fl6->daddr))
+		fl6->daddr.s6_addr[15] = 0x1; /* :: means loopback (BSD'ism) */
 
-	final_p = fl6_update_dst(&fl6, opt, &final);
+	final_p = fl6_update_dst(fl6, opt, &final);
 	if (final_p)
 		connected = false;
 
-	if (!fl6.flowi6_oif && ipv6_addr_is_multicast(&fl6.daddr)) {
-		fl6.flowi6_oif = np->mcast_oif;
+	if (!fl6->flowi6_oif && ipv6_addr_is_multicast(&fl6->daddr)) {
+		fl6->flowi6_oif = np->mcast_oif;
 		connected = false;
-	} else if (!fl6.flowi6_oif)
-		fl6.flowi6_oif = np->ucast_oif;
+	} else if (!fl6->flowi6_oif)
+		fl6->flowi6_oif = np->ucast_oif;
 
-	security_sk_classify_flow(sk, flowi6_to_flowi_common(&fl6));
+	security_sk_classify_flow(sk, flowi6_to_flowi_common(fl6));
 
 	if (ipc6.tclass < 0)
 		ipc6.tclass = np->tclass;
 
-	fl6.flowlabel = ip6_make_flowinfo(ipc6.tclass, fl6.flowlabel);
+	fl6->flowlabel = ip6_make_flowinfo(ipc6.tclass, fl6->flowlabel);
 
-	dst = ip6_sk_dst_lookup_flow(sk, &fl6, final_p, connected);
+	dst = ip6_sk_dst_lookup_flow(sk, fl6, final_p, connected);
 	if (IS_ERR(dst)) {
 		err = PTR_ERR(dst);
 		dst = NULL;
@@ -1522,7 +1524,7 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	}
 
 	if (ipc6.hlimit < 0)
-		ipc6.hlimit = ip6_sk_dst_hoplimit(np, &fl6, dst);
+		ipc6.hlimit = ip6_sk_dst_hoplimit(np, fl6, dst);
 
 	if (msg->msg_flags&MSG_CONFIRM)
 		goto do_confirm;
@@ -1530,18 +1532,15 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 
 	/* Lockless fast path for the non-corking case */
 	if (!corkreq) {
-		struct inet_cork_full cork;
 		struct sk_buff *skb;
 
-		cork.fl.u.ip6 = fl6;
-
 		skb = ip6_make_skb(sk, getfrag, msg, ulen,
 				   sizeof(struct udphdr), &ipc6,
 				   (struct rt6_info *)dst,
 				   msg->msg_flags, &cork);
 		err = PTR_ERR(skb);
 		if (!IS_ERR_OR_NULL(skb))
-			err = udp_v6_send_skb(skb, &fl6, &cork.base);
+			err = udp_v6_send_skb(skb, fl6, &cork.base);
 		goto out;
 	}
 
@@ -1563,7 +1562,7 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		ipc6.dontfrag = np->dontfrag;
 	up->len += ulen;
 	err = ip6_append_data(sk, getfrag, msg, ulen, sizeof(struct udphdr),
-			      &ipc6, &fl6, (struct rt6_info *)dst,
+			      &ipc6, fl6, (struct rt6_info *)dst,
 			      corkreq ? msg->msg_flags|MSG_MORE : msg->msg_flags);
 	if (err)
 		udp_v6_flush_pending_frames(sk);
@@ -1598,7 +1597,7 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 
 do_confirm:
 	if (msg->msg_flags & MSG_PROBE)
-		dst_confirm_neigh(dst, &fl6.daddr);
+		dst_confirm_neigh(dst, &fl6->daddr);
 	if (!(msg->msg_flags&MSG_PROBE) || len)
 		goto back_from_confirm;
 	err = 0;