Merge branch 'tcp-cong-undo_cwnd-mandatory'

Florian Westphal says:

====================
tcp: make undo_cwnd mandatory for congestion modules

highspeed, illinois, scalable, veno and yeah congestion control algorithms
don't provide a 'cwnd_undo' function.  This makes the stack default to a
'reno undo' which doubles cwnd.  However, the ssthresh implementation of
these algorithms do not halve the slowstart threshold. This causes similar
issue as the one fixed for dctcp in ce6dd23329b1e ("dctcp: avoid bogus
doubling of cwnd after loss").

In light of this it seems better to remove the fallback and make undo_cwnd
mandatory.

First patch fixes those spots where reno undo seems incorrect by providing
.cwnd_undo functions, second patch removes the fallback.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

13 files changed, 74 insertions, 7 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 123979fe12bf..7de80739adab 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -958,6 +958,7 @@ u32 tcp_slow_start(struct tcp_sock *tp, u32 acked);
 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);
 
 u32 tcp_reno_ssthresh(struct sock *sk);
+u32 tcp_reno_undo_cwnd(struct sock *sk);
 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked);
 extern struct tcp_congestion_ops tcp_reno;
 
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 1294af4e0127..38905ec5f508 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -68,8 +68,9 @@ int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
 {
 	int ret = 0;
 
-	/* all algorithms must implement ssthresh and cong_avoid ops */
-	if (!ca->ssthresh || !(ca->cong_avoid || ca->cong_control)) {
+	/* all algorithms must implement these */
+	if (!ca->ssthresh || !ca->undo_cwnd ||
+	    !(ca->cong_avoid || ca->cong_control)) {
 		pr_err("%s does not implement required ops\n", ca->name);
 		return -EINVAL;
 	}
@@ -441,10 +442,19 @@ u32 tcp_reno_ssthresh(struct sock *sk)
 }
 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
 
+u32 tcp_reno_undo_cwnd(struct sock *sk)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+
+	return max(tp->snd_cwnd, tp->snd_ssthresh << 1);
+}
+EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
+
 struct tcp_congestion_ops tcp_reno = {
 	.flags		= TCP_CONG_NON_RESTRICTED,
 	.name		= "reno",
 	.owner		= THIS_MODULE,
 	.ssthresh	= tcp_reno_ssthresh,
 	.cong_avoid	= tcp_reno_cong_avoid,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
 };
diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c
index 51139175bf61..bde22ebb92a8 100644
--- a/net/ipv4/tcp_dctcp.c
+++ b/net/ipv4/tcp_dctcp.c
@@ -342,6 +342,7 @@ static struct tcp_congestion_ops dctcp __read_mostly = {
 static struct tcp_congestion_ops dctcp_reno __read_mostly = {
 	.ssthresh	= tcp_reno_ssthresh,
 	.cong_avoid	= tcp_reno_cong_avoid,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
 	.get_info	= dctcp_get_info,
 	.owner		= THIS_MODULE,
 	.name		= "dctcp-reno",
diff --git a/net/ipv4/tcp_highspeed.c b/net/ipv4/tcp_highspeed.c
index db7842495a64..6d9879e93648 100644
--- a/net/ipv4/tcp_highspeed.c
+++ b/net/ipv4/tcp_highspeed.c
@@ -94,6 +94,7 @@ static const struct hstcp_aimd_val {
 
 struct hstcp {
 	u32	ai;
+	u32	loss_cwnd;
 };
 
 static void hstcp_init(struct sock *sk)
@@ -150,16 +151,24 @@ static void hstcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 static u32 hstcp_ssthresh(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
-	const struct hstcp *ca = inet_csk_ca(sk);
+	struct hstcp *ca = inet_csk_ca(sk);
 
+	ca->loss_cwnd = tp->snd_cwnd;
 	/* Do multiplicative decrease */
 	return max(tp->snd_cwnd - ((tp->snd_cwnd * hstcp_aimd_vals[ca->ai].md) >> 8), 2U);
 }
 
+static u32 hstcp_cwnd_undo(struct sock *sk)
+{
+	const struct hstcp *ca = inet_csk_ca(sk);
+
+	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
+}
 
 static struct tcp_congestion_ops tcp_highspeed __read_mostly = {
 	.init		= hstcp_init,
 	.ssthresh	= hstcp_ssthresh,
+	.undo_cwnd	= hstcp_cwnd_undo,
 	.cong_avoid	= hstcp_cong_avoid,
 
 	.owner		= THIS_MODULE,
diff --git a/net/ipv4/tcp_hybla.c b/net/ipv4/tcp_hybla.c
index 083831e359df..0f7175c3338e 100644
--- a/net/ipv4/tcp_hybla.c
+++ b/net/ipv4/tcp_hybla.c
@@ -166,6 +166,7 @@ static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 static struct tcp_congestion_ops tcp_hybla __read_mostly = {
 	.init		= hybla_init,
 	.ssthresh	= tcp_reno_ssthresh,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
 	.cong_avoid	= hybla_cong_avoid,
 	.set_state	= hybla_state,
 
diff --git a/net/ipv4/tcp_illinois.c b/net/ipv4/tcp_illinois.c
index c8e6d86be114..60352ff4f5a8 100644
--- a/net/ipv4/tcp_illinois.c
+++ b/net/ipv4/tcp_illinois.c
@@ -48,6 +48,7 @@ struct illinois {
 	u32	end_seq;	/* right edge of current RTT */
 	u32	alpha;		/* Additive increase */
 	u32	beta;		/* Muliplicative decrease */
+	u32	loss_cwnd;	/* cwnd on loss */
 	u16	acked;		/* # packets acked by current ACK */
 	u8	rtt_above;	/* average rtt has gone above threshold */
 	u8	rtt_low;	/* # of rtts measurements below threshold */
@@ -296,10 +297,18 @@ static u32 tcp_illinois_ssthresh(struct sock *sk)
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct illinois *ca = inet_csk_ca(sk);
 
+	ca->loss_cwnd = tp->snd_cwnd;
 	/* Multiplicative decrease */
 	return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U);
 }
 
+static u32 tcp_illinois_cwnd_undo(struct sock *sk)
+{
+	const struct illinois *ca = inet_csk_ca(sk);
+
+	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
+}
+
 /* Extract info for Tcp socket info provided via netlink. */
 static size_t tcp_illinois_info(struct sock *sk, u32 ext, int *attr,
 				union tcp_cc_info *info)
@@ -327,6 +336,7 @@ static size_t tcp_illinois_info(struct sock *sk, u32 ext, int *attr,
 static struct tcp_congestion_ops tcp_illinois __read_mostly = {
 	.init		= tcp_illinois_init,
 	.ssthresh	= tcp_illinois_ssthresh,
+	.undo_cwnd	= tcp_illinois_cwnd_undo,
 	.cong_avoid	= tcp_illinois_cong_avoid,
 	.set_state	= tcp_illinois_state,
 	.get_info	= tcp_illinois_info,
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a70046fea0e8..22e6a2097ff6 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2394,10 +2394,7 @@ static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
 	if (tp->prior_ssthresh) {
 		const struct inet_connection_sock *icsk = inet_csk(sk);
 
-		if (icsk->icsk_ca_ops->undo_cwnd)
-			tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
-		else
-			tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
+		tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
 
 		if (tp->prior_ssthresh > tp->snd_ssthresh) {
 			tp->snd_ssthresh = tp->prior_ssthresh;
diff --git a/net/ipv4/tcp_lp.c b/net/ipv4/tcp_lp.c
index c67ece1390c2..046fd3910873 100644
--- a/net/ipv4/tcp_lp.c
+++ b/net/ipv4/tcp_lp.c
@@ -316,6 +316,7 @@ static void tcp_lp_pkts_acked(struct sock *sk, const struct ack_sample *sample)
 static struct tcp_congestion_ops tcp_lp __read_mostly = {
 	.init = tcp_lp_init,
 	.ssthresh = tcp_reno_ssthresh,
+	.undo_cwnd = tcp_reno_undo_cwnd,
 	.cong_avoid = tcp_lp_cong_avoid,
 	.pkts_acked = tcp_lp_pkts_acked,
 
diff --git a/net/ipv4/tcp_scalable.c b/net/ipv4/tcp_scalable.c
index bf5ea9e9bbc1..f2123075ce6e 100644
--- a/net/ipv4/tcp_scalable.c
+++ b/net/ipv4/tcp_scalable.c
@@ -15,6 +15,10 @@
 #define TCP_SCALABLE_AI_CNT	50U
 #define TCP_SCALABLE_MD_SCALE	3
 
+struct scalable {
+	u32 loss_cwnd;
+};
+
 static void tcp_scalable_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
@@ -32,12 +36,23 @@ static void tcp_scalable_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 static u32 tcp_scalable_ssthresh(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
+	struct scalable *ca = inet_csk_ca(sk);
+
+	ca->loss_cwnd = tp->snd_cwnd;
 
 	return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);
 }
 
+static u32 tcp_scalable_cwnd_undo(struct sock *sk)
+{
+	const struct scalable *ca = inet_csk_ca(sk);
+
+	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
+}
+
 static struct tcp_congestion_ops tcp_scalable __read_mostly = {
 	.ssthresh	= tcp_scalable_ssthresh,
+	.undo_cwnd	= tcp_scalable_cwnd_undo,
 	.cong_avoid	= tcp_scalable_cong_avoid,
 
 	.owner		= THIS_MODULE,
diff --git a/net/ipv4/tcp_vegas.c b/net/ipv4/tcp_vegas.c
index 4c4bac1b5eab..218cfcc77650 100644
--- a/net/ipv4/tcp_vegas.c
+++ b/net/ipv4/tcp_vegas.c
@@ -307,6 +307,7 @@ EXPORT_SYMBOL_GPL(tcp_vegas_get_info);
 static struct tcp_congestion_ops tcp_vegas __read_mostly = {
 	.init		= tcp_vegas_init,
 	.ssthresh	= tcp_reno_ssthresh,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
 	.cong_avoid	= tcp_vegas_cong_avoid,
 	.pkts_acked	= tcp_vegas_pkts_acked,
 	.set_state	= tcp_vegas_state,
diff --git a/net/ipv4/tcp_veno.c b/net/ipv4/tcp_veno.c
index 40171e163cff..76005d4b8dfc 100644
--- a/net/ipv4/tcp_veno.c
+++ b/net/ipv4/tcp_veno.c
@@ -30,6 +30,7 @@ struct veno {
 	u32 basertt;		/* the min of all Veno rtt measurements seen (in usec) */
 	u32 inc;		/* decide whether to increase cwnd */
 	u32 diff;		/* calculate the diff rate */
+	u32 loss_cwnd;		/* cwnd when loss occured */
 };
 
 /* There are several situations when we must "re-start" Veno:
@@ -193,6 +194,7 @@ static u32 tcp_veno_ssthresh(struct sock *sk)
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct veno *veno = inet_csk_ca(sk);
 
+	veno->loss_cwnd = tp->snd_cwnd;
 	if (veno->diff < beta)
 		/* in "non-congestive state", cut cwnd by 1/5 */
 		return max(tp->snd_cwnd * 4 / 5, 2U);
@@ -201,9 +203,17 @@ static u32 tcp_veno_ssthresh(struct sock *sk)
 		return max(tp->snd_cwnd >> 1U, 2U);
 }
 
+static u32 tcp_veno_cwnd_undo(struct sock *sk)
+{
+	const struct veno *veno = inet_csk_ca(sk);
+
+	return max(tcp_sk(sk)->snd_cwnd, veno->loss_cwnd);
+}
+
 static struct tcp_congestion_ops tcp_veno __read_mostly = {
 	.init		= tcp_veno_init,
 	.ssthresh	= tcp_veno_ssthresh,
+	.undo_cwnd	= tcp_veno_cwnd_undo,
 	.cong_avoid	= tcp_veno_cong_avoid,
 	.pkts_acked	= tcp_veno_pkts_acked,
 	.set_state	= tcp_veno_state,
diff --git a/net/ipv4/tcp_westwood.c b/net/ipv4/tcp_westwood.c
index 4b03a2e2a050..fed66dc0e0f5 100644
--- a/net/ipv4/tcp_westwood.c
+++ b/net/ipv4/tcp_westwood.c
@@ -278,6 +278,7 @@ static struct tcp_congestion_ops tcp_westwood __read_mostly = {
 	.init		= tcp_westwood_init,
 	.ssthresh	= tcp_reno_ssthresh,
 	.cong_avoid	= tcp_reno_cong_avoid,
+	.undo_cwnd      = tcp_reno_undo_cwnd,
 	.cwnd_event	= tcp_westwood_event,
 	.in_ack_event	= tcp_westwood_ack,
 	.get_info	= tcp_westwood_info,
diff --git a/net/ipv4/tcp_yeah.c b/net/ipv4/tcp_yeah.c
index 9c5fc973267f..e6ff99c4bd3b 100644
--- a/net/ipv4/tcp_yeah.c
+++ b/net/ipv4/tcp_yeah.c
@@ -37,6 +37,7 @@ struct yeah {
 	u32 fast_count;
 
 	u32 pkts_acked;
+	u32 loss_cwnd;
 };
 
 static void tcp_yeah_init(struct sock *sk)
@@ -219,13 +220,22 @@ static u32 tcp_yeah_ssthresh(struct sock *sk)
 
 	yeah->fast_count = 0;
 	yeah->reno_count = max(yeah->reno_count>>1, 2U);
+	yeah->loss_cwnd = tp->snd_cwnd;
 
 	return max_t(int, tp->snd_cwnd - reduction, 2);
 }
 
+static u32 tcp_yeah_cwnd_undo(struct sock *sk)
+{
+	const struct yeah *yeah = inet_csk_ca(sk);
+
+	return max(tcp_sk(sk)->snd_cwnd, yeah->loss_cwnd);
+}
+
 static struct tcp_congestion_ops tcp_yeah __read_mostly = {
 	.init		= tcp_yeah_init,
 	.ssthresh	= tcp_yeah_ssthresh,
+	.undo_cwnd      = tcp_yeah_cwnd_undo,
 	.cong_avoid	= tcp_yeah_cong_avoid,
 	.set_state	= tcp_vegas_state,
 	.cwnd_event	= tcp_vegas_cwnd_event,