mptcp: optimize the input options processing

Most MPTCP packets carries a single MPTCP subption: the
DSS containing the mapping for the current packet.

Check explicitly for the above, so that is such scenario we
replace most conditional statements with a single likely() one.
Signed-off-by: NPaolo Abeni <pabeni@redhat.com>
Signed-off-by: NMat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/mptcp/options.c

@@ -1111,48 +1111,51 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 	if (!check_fully_established(msk, sk, subflow, skb, &mp_opt))
 		return sk->sk_state != TCP_CLOSE;
 
-	if ((mp_opt.suboptions & OPTION_MPTCP_FASTCLOSE) &&
-	    msk->local_key == mp_opt.rcvr_key) {
-		WRITE_ONCE(msk->rcv_fastclose, true);
-		mptcp_schedule_work((struct sock *)msk);
-	}
+	if (unlikely(mp_opt.suboptions != OPTION_MPTCP_DSS)) {
+		if ((mp_opt.suboptions & OPTION_MPTCP_FASTCLOSE) &&
+		    msk->local_key == mp_opt.rcvr_key) {
+			WRITE_ONCE(msk->rcv_fastclose, true);
+			mptcp_schedule_work((struct sock *)msk);
+		}
 
-	if ((mp_opt.suboptions & OPTION_MPTCP_ADD_ADDR) && add_addr_hmac_valid(msk, &mp_opt)) {
-		if (!mp_opt.echo) {
-			mptcp_pm_add_addr_received(msk, &mp_opt.addr);
-			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ADDADDR);
-		} else {
-			mptcp_pm_add_addr_echoed(msk, &mp_opt.addr);
-			mptcp_pm_del_add_timer(msk, &mp_opt.addr, true);
-			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ECHOADD);
+		if ((mp_opt.suboptions & OPTION_MPTCP_ADD_ADDR) &&
+		    add_addr_hmac_valid(msk, &mp_opt)) {
+			if (!mp_opt.echo) {
+				mptcp_pm_add_addr_received(msk, &mp_opt.addr);
+				MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ADDADDR);
+			} else {
+				mptcp_pm_add_addr_echoed(msk, &mp_opt.addr);
+				mptcp_pm_del_add_timer(msk, &mp_opt.addr, true);
+				MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ECHOADD);
+			}
+
+			if (mp_opt.addr.port)
+				MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_PORTADD);
 		}
 
-		if (mp_opt.addr.port)
-			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_PORTADD);
-	}
+		if (mp_opt.suboptions & OPTION_MPTCP_RM_ADDR)
+			mptcp_pm_rm_addr_received(msk, &mp_opt.rm_list);
 
-	if (mp_opt.suboptions & OPTION_MPTCP_RM_ADDR)
-		mptcp_pm_rm_addr_received(msk, &mp_opt.rm_list);
+		if (mp_opt.suboptions & OPTION_MPTCP_PRIO) {
+			mptcp_pm_mp_prio_received(sk, mp_opt.backup);
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPPRIORX);
+		}
 
-	if (mp_opt.suboptions & OPTION_MPTCP_PRIO) {
-		mptcp_pm_mp_prio_received(sk, mp_opt.backup);
-		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPPRIORX);
-	}
+		if (mp_opt.suboptions & OPTION_MPTCP_FAIL) {
+			mptcp_pm_mp_fail_received(sk, mp_opt.fail_seq);
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPFAILRX);
+		}
 
-	if (mp_opt.suboptions & OPTION_MPTCP_FAIL) {
-		mptcp_pm_mp_fail_received(sk, mp_opt.fail_seq);
-		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPFAILRX);
-	}
+		if (mp_opt.suboptions & OPTION_MPTCP_RST) {
+			subflow->reset_seen = 1;
+			subflow->reset_reason = mp_opt.reset_reason;
+			subflow->reset_transient = mp_opt.reset_transient;
+		}
 
-	if (mp_opt.suboptions & OPTION_MPTCP_RST) {
-		subflow->reset_seen = 1;
-		subflow->reset_reason = mp_opt.reset_reason;
-		subflow->reset_transient = mp_opt.reset_transient;
+		if (!(mp_opt.suboptions & OPTION_MPTCP_DSS))
+			return true;
 	}
 
-	if (!(mp_opt.suboptions & OPTION_MPTCP_DSS))
-		return true;
-
 	/* we can't wait for recvmsg() to update the ack_seq, otherwise
 	 * monodirectional flows will stuck
 	 */
@@ -1179,7 +1182,7 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 
 	memset(mpext, 0, sizeof(*mpext));
 
-	if (mp_opt.use_map) {
+	if (likely(mp_opt.use_map)) {
 		if (mp_opt.mpc_map) {
 			/* this is an MP_CAPABLE carrying MPTCP data
 			 * we know this map the first chunk of data