1 files changed, 148 insertions, 133 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index d377f48..432c366 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -237,7 +237,11 @@ static inline void TCP_ECN_check_ce(struct tcp_sock *tp, const struct sk_buff *s
 			tcp_enter_quickack_mode((struct sock *)tp);
 		break;
 	case INET_ECN_CE:
-		tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
+		if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
+			/* Better not delay acks, sender can have a very low cwnd */
+			tcp_enter_quickack_mode((struct sock *)tp);
+			tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
+		}
 		/* fallinto */
 	default:
 		tp->ecn_flags |= TCP_ECN_SEEN;
@@ -374,7 +378,7 @@ static void tcp_fixup_rcvbuf(struct sock *sk)
 /* 4. Try to fixup all. It is made immediately after connection enters
  *    established state.
  */
-static void tcp_init_buffer_space(struct sock *sk)
+void tcp_init_buffer_space(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	int maxwin;
@@ -739,29 +743,6 @@ __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
 	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
 }
 
-/* Set slow start threshold and cwnd not falling to slow start */
-void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
-{
-	struct tcp_sock *tp = tcp_sk(sk);
-	const struct inet_connection_sock *icsk = inet_csk(sk);
-
-	tp->prior_ssthresh = 0;
-	tp->bytes_acked = 0;
-	if (icsk->icsk_ca_state < TCP_CA_CWR) {
-		tp->undo_marker = 0;
-		if (set_ssthresh)
-			tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
-		tp->snd_cwnd = min(tp->snd_cwnd,
-				   tcp_packets_in_flight(tp) + 1U);
-		tp->snd_cwnd_cnt = 0;
-		tp->high_seq = tp->snd_nxt;
-		tp->snd_cwnd_stamp = tcp_time_stamp;
-		TCP_ECN_queue_cwr(tp);
-
-		tcp_set_ca_state(sk, TCP_CA_CWR);
-	}
-}
-
 /*
  * Packet counting of FACK is based on in-order assumptions, therefore TCP
  * disables it when reordering is detected
@@ -2489,35 +2470,6 @@ static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
 	tp->snd_cwnd_stamp = tcp_time_stamp;
 }
 
-/* Lower bound on congestion window is slow start threshold
- * unless congestion avoidance choice decides to overide it.
- */
-static inline u32 tcp_cwnd_min(const struct sock *sk)
-{
-	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
-
-	return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
-}
-
-/* Decrease cwnd each second ack. */
-static void tcp_cwnd_down(struct sock *sk, int flag)
-{
-	struct tcp_sock *tp = tcp_sk(sk);
-	int decr = tp->snd_cwnd_cnt + 1;
-
-	if ((flag & (FLAG_ANY_PROGRESS | FLAG_DSACKING_ACK)) ||
-	    (tcp_is_reno(tp) && !(flag & FLAG_NOT_DUP))) {
-		tp->snd_cwnd_cnt = decr & 1;
-		decr >>= 1;
-
-		if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
-			tp->snd_cwnd -= decr;
-
-		tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
-		tp->snd_cwnd_stamp = tcp_time_stamp;
-	}
-}
-
 /* Nothing was retransmitted or returned timestamp is less
  * than timestamp of the first retransmission.
  */
@@ -2719,24 +2671,80 @@ static bool tcp_try_undo_loss(struct sock *sk)
 	return false;
 }
 
-static inline void tcp_complete_cwr(struct sock *sk)
+/* The cwnd reduction in CWR and Recovery use the PRR algorithm
+ * https://datatracker.ietf.org/doc/draft-ietf-tcpm-proportional-rate-reduction/
+ * It computes the number of packets to send (sndcnt) based on packets newly
+ * delivered:
+ *   1) If the packets in flight is larger than ssthresh, PRR spreads the
+ *	cwnd reductions across a full RTT.
+ *   2) If packets in flight is lower than ssthresh (such as due to excess
+ *	losses and/or application stalls), do not perform any further cwnd
+ *	reductions, but instead slow start up to ssthresh.
+ */
+static void tcp_init_cwnd_reduction(struct sock *sk, const bool set_ssthresh)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	/* Do not moderate cwnd if it's already undone in cwr or recovery. */
-	if (tp->undo_marker) {
-		if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR) {
-			tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
-			tp->snd_cwnd_stamp = tcp_time_stamp;
-		} else if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH) {
-			/* PRR algorithm. */
-			tp->snd_cwnd = tp->snd_ssthresh;
-			tp->snd_cwnd_stamp = tcp_time_stamp;
-		}
+	tp->high_seq = tp->snd_nxt;
+	tp->bytes_acked = 0;
+	tp->snd_cwnd_cnt = 0;
+	tp->prior_cwnd = tp->snd_cwnd;
+	tp->prr_delivered = 0;
+	tp->prr_out = 0;
+	if (set_ssthresh)
+		tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
+	TCP_ECN_queue_cwr(tp);
+}
+
+static void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked,
+			       int fast_rexmit)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	int sndcnt = 0;
+	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
+
+	tp->prr_delivered += newly_acked_sacked;
+	if (tcp_packets_in_flight(tp) > tp->snd_ssthresh) {
+		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
+			       tp->prior_cwnd - 1;
+		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
+	} else {
+		sndcnt = min_t(int, delta,
+			       max_t(int, tp->prr_delivered - tp->prr_out,
+				     newly_acked_sacked) + 1);
+	}
+
+	sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
+	tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
+}
+
+static inline void tcp_end_cwnd_reduction(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
+	if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
+	    (tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
+		tp->snd_cwnd = tp->snd_ssthresh;
+		tp->snd_cwnd_stamp = tcp_time_stamp;
 	}
 	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
 }
 
+/* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
+void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	tp->prior_ssthresh = 0;
+	tp->bytes_acked = 0;
+	if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
+		tp->undo_marker = 0;
+		tcp_init_cwnd_reduction(sk, set_ssthresh);
+		tcp_set_ca_state(sk, TCP_CA_CWR);
+	}
+}
+
 static void tcp_try_keep_open(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
@@ -2751,7 +2759,7 @@ static void tcp_try_keep_open(struct sock *sk)
 	}
 }
 
-static void tcp_try_to_open(struct sock *sk, int flag)
+static void tcp_try_to_open(struct sock *sk, int flag, int newly_acked_sacked)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
@@ -2768,7 +2776,7 @@ static void tcp_try_to_open(struct sock *sk, int flag)
 		if (inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
 			tcp_moderate_cwnd(tp);
 	} else {
-		tcp_cwnd_down(sk, flag);
+		tcp_cwnd_reduction(sk, newly_acked_sacked, 0);
 	}
 }
 
@@ -2850,38 +2858,6 @@ void tcp_simple_retransmit(struct sock *sk)
 }
 EXPORT_SYMBOL(tcp_simple_retransmit);
 
-/* This function implements the PRR algorithm, specifcally the PRR-SSRB
- * (proportional rate reduction with slow start reduction bound) as described in
- * http://www.ietf.org/id/draft-mathis-tcpm-proportional-rate-reduction-01.txt.
- * It computes the number of packets to send (sndcnt) based on packets newly
- * delivered:
- *   1) If the packets in flight is larger than ssthresh, PRR spreads the
- *	cwnd reductions across a full RTT.
- *   2) If packets in flight is lower than ssthresh (such as due to excess
- *	losses and/or application stalls), do not perform any further cwnd
- *	reductions, but instead slow start up to ssthresh.
- */
-static void tcp_update_cwnd_in_recovery(struct sock *sk, int newly_acked_sacked,
-					int fast_rexmit, int flag)
-{
-	struct tcp_sock *tp = tcp_sk(sk);
-	int sndcnt = 0;
-	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
-
-	if (tcp_packets_in_flight(tp) > tp->snd_ssthresh) {
-		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
-			       tp->prior_cwnd - 1;
-		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
-	} else {
-		sndcnt = min_t(int, delta,
-			       max_t(int, tp->prr_delivered - tp->prr_out,
-				     newly_acked_sacked) + 1);
-	}
-
-	sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
-	tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
-}
-
 static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
@@ -2894,7 +2870,6 @@ static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
 
 	NET_INC_STATS_BH(sock_net(sk), mib_idx);
 
-	tp->high_seq = tp->snd_nxt;
 	tp->prior_ssthresh = 0;
 	tp->undo_marker = tp->snd_una;
 	tp->undo_retrans = tp->retrans_out;
@@ -2902,15 +2877,8 @@ static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
 	if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
 		if (!ece_ack)
 			tp->prior_ssthresh = tcp_current_ssthresh(sk);
-		tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
-		TCP_ECN_queue_cwr(tp);
+		tcp_init_cwnd_reduction(sk, true);
 	}
-
-	tp->bytes_acked = 0;
-	tp->snd_cwnd_cnt = 0;
-	tp->prior_cwnd = tp->snd_cwnd;
-	tp->prr_delivered = 0;
-	tp->prr_out = 0;
 	tcp_set_ca_state(sk, TCP_CA_Recovery);
 }
 
@@ -2970,7 +2938,7 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
 			/* CWR is to be held something *above* high_seq
 			 * is ACKed for CWR bit to reach receiver. */
 			if (tp->snd_una != tp->high_seq) {
-				tcp_complete_cwr(sk);
+				tcp_end_cwnd_reduction(sk);
 				tcp_set_ca_state(sk, TCP_CA_Open);
 			}
 			break;
@@ -2980,7 +2948,7 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
 				tcp_reset_reno_sack(tp);
 			if (tcp_try_undo_recovery(sk))
 				return;
-			tcp_complete_cwr(sk);
+			tcp_end_cwnd_reduction(sk);
 			break;
 		}
 	}
@@ -3021,7 +2989,7 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
 			tcp_try_undo_dsack(sk);
 
 		if (!tcp_time_to_recover(sk, flag)) {
-			tcp_try_to_open(sk, flag);
+			tcp_try_to_open(sk, flag, newly_acked_sacked);
 			return;
 		}
 
@@ -3043,8 +3011,7 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
 
 	if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk)))
 		tcp_update_scoreboard(sk, fast_rexmit);
-	tp->prr_delivered += newly_acked_sacked;
-	tcp_update_cwnd_in_recovery(sk, newly_acked_sacked, fast_rexmit, flag);
+	tcp_cwnd_reduction(sk, newly_acked_sacked, fast_rexmit);
 	tcp_xmit_retransmit_queue(sk);
 }
 
@@ -3123,6 +3090,12 @@ void tcp_rearm_rto(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
+	/* If the retrans timer is currently being used by Fast Open
+	 * for SYN-ACK retrans purpose, stay put.
+	 */
+	if (tp->fastopen_rsk)
+		return;
+
 	if (!tp->packets_out) {
 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
 	} else {
@@ -3384,7 +3357,7 @@ static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
-		!((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
+		!tcp_in_cwnd_reduction(sk);
 }
 
 /* Check that window update is acceptable.
@@ -3452,9 +3425,9 @@ static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
 }
 
 /* A conservative spurious RTO response algorithm: reduce cwnd using
- * rate halving and continue in congestion avoidance.
+ * PRR and continue in congestion avoidance.
  */
-static void tcp_ratehalving_spur_to_response(struct sock *sk)
+static void tcp_cwr_spur_to_response(struct sock *sk)
 {
 	tcp_enter_cwr(sk, 0);
 }
@@ -3462,7 +3435,7 @@ static void tcp_ratehalving_spur_to_response(struct sock *sk)
 static void tcp_undo_spur_to_response(struct sock *sk, int flag)
 {
 	if (flag & FLAG_ECE)
-		tcp_ratehalving_spur_to_response(sk);
+		tcp_cwr_spur_to_response(sk);
 	else
 		tcp_undo_cwr(sk, true);
 }
@@ -3569,7 +3542,7 @@ static bool tcp_process_frto(struct sock *sk, int flag)
 			tcp_conservative_spur_to_response(tp);
 			break;
 		default:
-			tcp_ratehalving_spur_to_response(sk);
+			tcp_cwr_spur_to_response(sk);
 			break;
 		}
 		tp->frto_counter = 0;
@@ -4034,7 +4007,7 @@ static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
 }
 
 /* When we get a reset we do this. */
-static void tcp_reset(struct sock *sk)
+void tcp_reset(struct sock *sk)
 {
 	/* We want the right error as BSD sees it (and indeed as we do). */
 	switch (sk->sk_state) {
@@ -5740,7 +5713,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 
 		TCP_ECN_rcv_synack(tp, th);
 
-		tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
+		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
 		tcp_ack(sk, skb, FLAG_SLOWPATH);
 
 		/* Ok.. it's good. Set up sequence numbers and
@@ -5753,7 +5726,6 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 		 * never scaled.
 		 */
 		tp->snd_wnd = ntohs(th->window);
-		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
 
 		if (!tp->rx_opt.wscale_ok) {
 			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
@@ -5891,7 +5863,9 @@ discard:
 		tcp_send_synack(sk);
 #if 0
 		/* Note, we could accept data and URG from this segment.
-		 * There are no obstacles to make this.
+		 * There are no obstacles to make this (except that we must
+		 * either change tcp_recvmsg() to prevent it from returning data
+		 * before 3WHS completes per RFC793, or employ TCP Fast Open).
 		 *
 		 * However, if we ignore data in ACKless segments sometimes,
 		 * we have no reasons to accept it sometimes.
@@ -5931,6 +5905,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct request_sock *req;
 	int queued = 0;
 
 	tp->rx_opt.saw_tstamp = 0;
@@ -5986,6 +5961,14 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 		return 0;
 	}
 
+	req = tp->fastopen_rsk;
+	if (req != NULL) {
+		BUG_ON(sk->sk_state != TCP_SYN_RECV &&
+		    sk->sk_state != TCP_FIN_WAIT1);
+
+		if (tcp_check_req(sk, skb, req, NULL, true) == NULL)
+			goto discard;
+	}
 	if (!tcp_validate_incoming(sk, skb, th, 0))
 		return 0;
 
@@ -5996,7 +5979,25 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 		switch (sk->sk_state) {
 		case TCP_SYN_RECV:
 			if (acceptable) {
-				tp->copied_seq = tp->rcv_nxt;
+				/* Once we leave TCP_SYN_RECV, we no longer
+				 * need req so release it.
+				 */
+				if (req) {
+					tcp_synack_rtt_meas(sk, req);
+					tp->total_retrans = req->retrans;
+
+					reqsk_fastopen_remove(sk, req, false);
+				} else {
+					/* Make sure socket is routed, for
+					 * correct metrics.
+					 */
+					icsk->icsk_af_ops->rebuild_header(sk);
+					tcp_init_congestion_control(sk);
+
+					tcp_mtup_init(sk);
+					tcp_init_buffer_space(sk);
+					tp->copied_seq = tp->rcv_nxt;
+				}
 				smp_mb();
 				tcp_set_state(sk, TCP_ESTABLISHED);
 				sk->sk_state_change(sk);
@@ -6018,23 +6019,27 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 				if (tp->rx_opt.tstamp_ok)
 					tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
 
-				/* Make sure socket is routed, for
-				 * correct metrics.
-				 */
-				icsk->icsk_af_ops->rebuild_header(sk);
-
-				tcp_init_metrics(sk);
-
-				tcp_init_congestion_control(sk);
+				if (req) {
+					/* Re-arm the timer because data may
+					 * have been sent out. This is similar
+					 * to the regular data transmission case
+					 * when new data has just been ack'ed.
+					 *
+					 * (TFO) - we could try to be more
+					 * aggressive and retranmitting any data
+					 * sooner based on when they were sent
+					 * out.
+					 */
+					tcp_rearm_rto(sk);
+				} else
+					tcp_init_metrics(sk);
 
 				/* Prevent spurious tcp_cwnd_restart() on
 				 * first data packet.
 				 */
 				tp->lsndtime = tcp_time_stamp;
 
-				tcp_mtup_init(sk);
 				tcp_initialize_rcv_mss(sk);
-				tcp_init_buffer_space(sk);
 				tcp_fast_path_on(tp);
 			} else {
 				return 1;
@@ -6042,6 +6047,16 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 			break;
 
 		case TCP_FIN_WAIT1:
+			/* If we enter the TCP_FIN_WAIT1 state and we are a
+			 * Fast Open socket and this is the first acceptable
+			 * ACK we have received, this would have acknowledged
+			 * our SYNACK so stop the SYNACK timer.
+			 */
+			if (acceptable && req != NULL) {
+				/* We no longer need the request sock. */
+				reqsk_fastopen_remove(sk, req, false);
+				tcp_rearm_rto(sk);
+			}
 			if (tp->snd_una == tp->write_seq) {
 				struct dst_entry *dst;