1 files changed, 4 insertions, 371 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 19f0149fb6a2..231c79fe91f3 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -93,7 +93,6 @@ int sysctl_tcp_stdurg __read_mostly;
 int sysctl_tcp_rfc1337 __read_mostly;
 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
 int sysctl_tcp_frto __read_mostly = 2;
-int sysctl_tcp_frto_response __read_mostly;
 
 int sysctl_tcp_thin_dupack __read_mostly;
 
@@ -108,17 +107,14 @@ int sysctl_tcp_early_retrans __read_mostly = 3;
 #define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
 #define FLAG_ECE		0x40 /* ECE in this ACK				*/
 #define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
-#define FLAG_ONLY_ORIG_SACKED	0x200 /* SACKs only non-rexmit sent before RTO */
 #define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
 #define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained D-SACK info */
-#define FLAG_NONHEAD_RETRANS_ACKED	0x1000 /* Non-head rexmitted data was ACKed */
 #define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */
 
 #define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
 #define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
 #define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE)
 #define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
-#define FLAG_ANY_PROGRESS	(FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
 
 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
@@ -1159,10 +1155,6 @@ static u8 tcp_sacktag_one(struct sock *sk,
 					   tcp_highest_sack_seq(tp)))
 					state->reord = min(fack_count,
 							   state->reord);
-
-				/* SACK enhanced F-RTO (RFC4138; Appendix B) */
-				if (!after(end_seq, tp->frto_highmark))
-					state->flag |= FLAG_ONLY_ORIG_SACKED;
 			}
 
 			if (sacked & TCPCB_LOST) {
@@ -1555,7 +1547,6 @@ static int
 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
 			u32 prior_snd_una)
 {
-	const struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 	const unsigned char *ptr = (skb_transport_header(ack_skb) +
 				    TCP_SKB_CB(ack_skb)->sacked);
@@ -1728,12 +1719,6 @@ walk:
 				       start_seq, end_seq, dup_sack);
 
 advance_sp:
-		/* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct
-		 * due to in-order walk
-		 */
-		if (after(end_seq, tp->frto_highmark))
-			state.flag &= ~FLAG_ONLY_ORIG_SACKED;
-
 		i++;
 	}
 
@@ -1750,8 +1735,7 @@ advance_sp:
 	tcp_verify_left_out(tp);
 
 	if ((state.reord < tp->fackets_out) &&
-	    ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) &&
-	    (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
+	    ((inet_csk(sk)->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker))
 		tcp_update_reordering(sk, tp->fackets_out - state.reord, 0);
 
 out:
@@ -1825,197 +1809,6 @@ static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
 	tp->sacked_out = 0;
 }
 
-static int tcp_is_sackfrto(const struct tcp_sock *tp)
-{
-	return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp);
-}
-
-/* F-RTO can only be used if TCP has never retransmitted anything other than
- * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
- */
-bool tcp_use_frto(struct sock *sk)
-{
-	const struct tcp_sock *tp = tcp_sk(sk);
-	const struct inet_connection_sock *icsk = inet_csk(sk);
-	struct sk_buff *skb;
-
-	if (!sysctl_tcp_frto)
-		return false;
-
-	/* MTU probe and F-RTO won't really play nicely along currently */
-	if (icsk->icsk_mtup.probe_size)
-		return false;
-
-	if (tcp_is_sackfrto(tp))
-		return true;
-
-	/* Avoid expensive walking of rexmit queue if possible */
-	if (tp->retrans_out > 1)
-		return false;
-
-	skb = tcp_write_queue_head(sk);
-	if (tcp_skb_is_last(sk, skb))
-		return true;
-	skb = tcp_write_queue_next(sk, skb);	/* Skips head */
-	tcp_for_write_queue_from(skb, sk) {
-		if (skb == tcp_send_head(sk))
-			break;
-		if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
-			return false;
-		/* Short-circuit when first non-SACKed skb has been checked */
-		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
-			break;
-	}
-	return true;
-}
-
-/* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
- * recovery a bit and use heuristics in tcp_process_frto() to detect if
- * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
- * keep retrans_out counting accurate (with SACK F-RTO, other than head
- * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
- * bits are handled if the Loss state is really to be entered (in
- * tcp_enter_frto_loss).
- *
- * Do like tcp_enter_loss() would; when RTO expires the second time it
- * does:
- *  "Reduce ssthresh if it has not yet been made inside this window."
- */
-void tcp_enter_frto(struct sock *sk)
-{
-	const struct inet_connection_sock *icsk = inet_csk(sk);
-	struct tcp_sock *tp = tcp_sk(sk);
-	struct sk_buff *skb;
-
-	if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
-	    tp->snd_una == tp->high_seq ||
-	    ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
-	     !icsk->icsk_retransmits)) {
-		tp->prior_ssthresh = tcp_current_ssthresh(sk);
-		/* Our state is too optimistic in ssthresh() call because cwnd
-		 * is not reduced until tcp_enter_frto_loss() when previous F-RTO
-		 * recovery has not yet completed. Pattern would be this: RTO,
-		 * Cumulative ACK, RTO (2xRTO for the same segment does not end
-		 * up here twice).
-		 * RFC4138 should be more specific on what to do, even though
-		 * RTO is quite unlikely to occur after the first Cumulative ACK
-		 * due to back-off and complexity of triggering events ...
-		 */
-		if (tp->frto_counter) {
-			u32 stored_cwnd;
-			stored_cwnd = tp->snd_cwnd;
-			tp->snd_cwnd = 2;
-			tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
-			tp->snd_cwnd = stored_cwnd;
-		} else {
-			tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
-		}
-		/* ... in theory, cong.control module could do "any tricks" in
-		 * ssthresh(), which means that ca_state, lost bits and lost_out
-		 * counter would have to be faked before the call occurs. We
-		 * consider that too expensive, unlikely and hacky, so modules
-		 * using these in ssthresh() must deal these incompatibility
-		 * issues if they receives CA_EVENT_FRTO and frto_counter != 0
-		 */
-		tcp_ca_event(sk, CA_EVENT_FRTO);
-	}
-
-	tp->undo_marker = tp->snd_una;
-	tp->undo_retrans = 0;
-
-	skb = tcp_write_queue_head(sk);
-	if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
-		tp->undo_marker = 0;
-	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
-		TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
-		tp->retrans_out -= tcp_skb_pcount(skb);
-	}
-	tcp_verify_left_out(tp);
-
-	/* Too bad if TCP was application limited */
-	tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
-
-	/* Earlier loss recovery underway (see RFC4138; Appendix B).
-	 * The last condition is necessary at least in tp->frto_counter case.
-	 */
-	if (tcp_is_sackfrto(tp) && (tp->frto_counter ||
-	    ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
-	    after(tp->high_seq, tp->snd_una)) {
-		tp->frto_highmark = tp->high_seq;
-	} else {
-		tp->frto_highmark = tp->snd_nxt;
-	}
-	tcp_set_ca_state(sk, TCP_CA_Disorder);
-	tp->high_seq = tp->snd_nxt;
-	tp->frto_counter = 1;
-}
-
-/* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
- * which indicates that we should follow the traditional RTO recovery,
- * i.e. mark everything lost and do go-back-N retransmission.
- */
-static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
-{
-	struct tcp_sock *tp = tcp_sk(sk);
-	struct sk_buff *skb;
-
-	tp->lost_out = 0;
-	tp->retrans_out = 0;
-	if (tcp_is_reno(tp))
-		tcp_reset_reno_sack(tp);
-
-	tcp_for_write_queue(skb, sk) {
-		if (skb == tcp_send_head(sk))
-			break;
-
-		TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
-		/*
-		 * Count the retransmission made on RTO correctly (only when
-		 * waiting for the first ACK and did not get it)...
-		 */
-		if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) {
-			/* For some reason this R-bit might get cleared? */
-			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
-				tp->retrans_out += tcp_skb_pcount(skb);
-			/* ...enter this if branch just for the first segment */
-			flag |= FLAG_DATA_ACKED;
-		} else {
-			if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
-				tp->undo_marker = 0;
-			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
-		}
-
-		/* Marking forward transmissions that were made after RTO lost
-		 * can cause unnecessary retransmissions in some scenarios,
-		 * SACK blocks will mitigate that in some but not in all cases.
-		 * We used to not mark them but it was causing break-ups with
-		 * receivers that do only in-order receival.
-		 *
-		 * TODO: we could detect presence of such receiver and select
-		 * different behavior per flow.
-		 */
-		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
-			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
-			tp->lost_out += tcp_skb_pcount(skb);
-			tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
-		}
-	}
-	tcp_verify_left_out(tp);
-
-	tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
-	tp->snd_cwnd_cnt = 0;
-	tp->snd_cwnd_stamp = tcp_time_stamp;
-	tp->frto_counter = 0;
-
-	tp->reordering = min_t(unsigned int, tp->reordering,
-			       sysctl_tcp_reordering);
-	tcp_set_ca_state(sk, TCP_CA_Loss);
-	tp->high_seq = tp->snd_nxt;
-	TCP_ECN_queue_cwr(tp);
-
-	tcp_clear_all_retrans_hints(tp);
-}
-
 static void tcp_clear_retrans_partial(struct tcp_sock *tp)
 {
 	tp->retrans_out = 0;
@@ -2090,8 +1883,6 @@ void tcp_enter_loss(struct sock *sk, int how)
 	tcp_set_ca_state(sk, TCP_CA_Loss);
 	tp->high_seq = tp->snd_nxt;
 	TCP_ECN_queue_cwr(tp);
-	/* Abort F-RTO algorithm if one is in progress */
-	tp->frto_counter = 0;
 }
 
 /* If ACK arrived pointing to a remembered SACK, it means that our
@@ -2275,10 +2066,6 @@ static bool tcp_time_to_recover(struct sock *sk, int flag)
 	struct tcp_sock *tp = tcp_sk(sk);
 	__u32 packets_out;
 
-	/* Do not perform any recovery during F-RTO algorithm */
-	if (tp->frto_counter)
-		return false;
-
 	/* Trick#1: The loss is proven. */
 	if (tp->lost_out)
 		return true;
@@ -2760,7 +2547,7 @@ static void tcp_try_to_open(struct sock *sk, int flag, int newly_acked_sacked)
 
 	tcp_verify_left_out(tp);
 
-	if (!tp->frto_counter && !tcp_any_retrans_done(sk))
+	if (!tcp_any_retrans_done(sk))
 		tp->retrans_stamp = 0;
 
 	if (flag & FLAG_ECE)
@@ -3198,8 +2985,6 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 			flag |= FLAG_RETRANS_DATA_ACKED;
 			ca_seq_rtt = -1;
 			seq_rtt = -1;
-			if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1))
-				flag |= FLAG_NONHEAD_RETRANS_ACKED;
 		} else {
 			ca_seq_rtt = now - scb->when;
 			last_ackt = skb->tstamp;
@@ -3408,150 +3193,6 @@ static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32
 	return flag;
 }
 
-/* A very conservative spurious RTO response algorithm: reduce cwnd and
- * continue in congestion avoidance.
- */
-static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
-{
-	tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
-	tp->snd_cwnd_cnt = 0;
-	TCP_ECN_queue_cwr(tp);
-	tcp_moderate_cwnd(tp);
-}
-
-/* A conservative spurious RTO response algorithm: reduce cwnd using
- * PRR and continue in congestion avoidance.
- */
-static void tcp_cwr_spur_to_response(struct sock *sk)
-{
-	tcp_enter_cwr(sk, 0);
-}
-
-static void tcp_undo_spur_to_response(struct sock *sk, int flag)
-{
-	if (flag & FLAG_ECE)
-		tcp_cwr_spur_to_response(sk);
-	else
-		tcp_undo_cwr(sk, true);
-}
-
-/* F-RTO spurious RTO detection algorithm (RFC4138)
- *
- * F-RTO affects during two new ACKs following RTO (well, almost, see inline
- * comments). State (ACK number) is kept in frto_counter. When ACK advances
- * window (but not to or beyond highest sequence sent before RTO):
- *   On First ACK,  send two new segments out.
- *   On Second ACK, RTO was likely spurious. Do spurious response (response
- *                  algorithm is not part of the F-RTO detection algorithm
- *                  given in RFC4138 but can be selected separately).
- * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
- * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
- * of Nagle, this is done using frto_counter states 2 and 3, when a new data
- * segment of any size sent during F-RTO, state 2 is upgraded to 3.
- *
- * Rationale: if the RTO was spurious, new ACKs should arrive from the
- * original window even after we transmit two new data segments.
- *
- * SACK version:
- *   on first step, wait until first cumulative ACK arrives, then move to
- *   the second step. In second step, the next ACK decides.
- *
- * F-RTO is implemented (mainly) in four functions:
- *   - tcp_use_frto() is used to determine if TCP is can use F-RTO
- *   - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
- *     called when tcp_use_frto() showed green light
- *   - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
- *   - tcp_enter_frto_loss() is called if there is not enough evidence
- *     to prove that the RTO is indeed spurious. It transfers the control
- *     from F-RTO to the conventional RTO recovery
- */
-static bool tcp_process_frto(struct sock *sk, int flag)
-{
-	struct tcp_sock *tp = tcp_sk(sk);
-
-	tcp_verify_left_out(tp);
-
-	/* Duplicate the behavior from Loss state (fastretrans_alert) */
-	if (flag & FLAG_DATA_ACKED)
-		inet_csk(sk)->icsk_retransmits = 0;
-
-	if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
-	    ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
-		tp->undo_marker = 0;
-
-	if (!before(tp->snd_una, tp->frto_highmark)) {
-		tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
-		return true;
-	}
-
-	if (!tcp_is_sackfrto(tp)) {
-		/* RFC4138 shortcoming in step 2; should also have case c):
-		 * ACK isn't duplicate nor advances window, e.g., opposite dir
-		 * data, winupdate
-		 */
-		if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP))
-			return true;
-
-		if (!(flag & FLAG_DATA_ACKED)) {
-			tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
-					    flag);
-			return true;
-		}
-	} else {
-		if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
-			if (!tcp_packets_in_flight(tp)) {
-				tcp_enter_frto_loss(sk, 2, flag);
-				return true;
-			}
-
-			/* Prevent sending of new data. */
-			tp->snd_cwnd = min(tp->snd_cwnd,
-					   tcp_packets_in_flight(tp));
-			return true;
-		}
-
-		if ((tp->frto_counter >= 2) &&
-		    (!(flag & FLAG_FORWARD_PROGRESS) ||
-		     ((flag & FLAG_DATA_SACKED) &&
-		      !(flag & FLAG_ONLY_ORIG_SACKED)))) {
-			/* RFC4138 shortcoming (see comment above) */
-			if (!(flag & FLAG_FORWARD_PROGRESS) &&
-			    (flag & FLAG_NOT_DUP))
-				return true;
-
-			tcp_enter_frto_loss(sk, 3, flag);
-			return true;
-		}
-	}
-
-	if (tp->frto_counter == 1) {
-		/* tcp_may_send_now needs to see updated state */
-		tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
-		tp->frto_counter = 2;
-
-		if (!tcp_may_send_now(sk))
-			tcp_enter_frto_loss(sk, 2, flag);
-
-		return true;
-	} else {
-		switch (sysctl_tcp_frto_response) {
-		case 2:
-			tcp_undo_spur_to_response(sk, flag);
-			break;
-		case 1:
-			tcp_conservative_spur_to_response(tp);
-			break;
-		default:
-			tcp_cwr_spur_to_response(sk);
-			break;
-		}
-		tp->frto_counter = 0;
-		tp->undo_marker = 0;
-		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSPURIOUSRTOS);
-	}
-	return false;
-}
-
 /* RFC 5961 7 [ACK Throttling] */
 static void tcp_send_challenge_ack(struct sock *sk)
 {
@@ -3616,7 +3257,6 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 	int prior_packets;
 	int prior_sacked = tp->sacked_out;
 	int pkts_acked = 0;
-	bool frto_cwnd = false;
 
 	/* If the ack is older than previous acks
 	 * then we can probably ignore it.
@@ -3690,22 +3330,15 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 
 	pkts_acked = prior_packets - tp->packets_out;
 
-	if (tp->frto_counter)
-		frto_cwnd = tcp_process_frto(sk, flag);
-	/* Guarantee sacktag reordering detection against wrap-arounds */
-	if (before(tp->frto_highmark, tp->snd_una))
-		tp->frto_highmark = 0;
-
 	if (tcp_ack_is_dubious(sk, flag)) {
 		/* Advance CWND, if state allows this. */
-		if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
-		    tcp_may_raise_cwnd(sk, flag))
+		if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(sk, flag))
 			tcp_cong_avoid(sk, ack, prior_in_flight);
 		is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
 		tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
 				      is_dupack, flag);
 	} else {
-		if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
+		if (flag & FLAG_DATA_ACKED)
 			tcp_cong_avoid(sk, ack, prior_in_flight);
 	}