From 4faf783998b8cb88294e9df89032f473f8771b78 Mon Sep 17 00:00:00 2001 From: Yuchung Cheng Date: Thu, 3 Aug 2017 20:38:51 -0700 Subject: [PATCH] tcp: fix cwnd undo in Reno and HTCP congestion controls Using ssthresh to revert cwnd is less reliable when ssthresh is bounded to 2 packets. This patch uses an existing variable in TCP "prior_cwnd" that snapshots the cwnd right before entering fast recovery and RTO recovery in Reno. This fixes the issue discussed in netdev thread: "A buggy behavior for Linux TCP Reno and HTCP" https://www.spinics.net/lists/netdev/msg444955.html Suggested-by: Neal Cardwell Reported-by: Wei Sun Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: David S. Miller --- include/linux/tcp.h | 2 +- net/ipv4/tcp_cong.c | 2 +- net/ipv4/tcp_htcp.c | 3 +-- net/ipv4/tcp_input.c | 1 + 4 files changed, 4 insertions(+), 4 deletions(-) diff --git a/include/linux/tcp.h b/include/linux/tcp.h index d7389ea..267164a 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -258,7 +258,7 @@ struct tcp_sock { u32 snd_cwnd_clamp; /* Do not allow snd_cwnd to grow above this */ u32 snd_cwnd_used; u32 snd_cwnd_stamp; - u32 prior_cwnd; /* Congestion window at start of Recovery. */ + u32 prior_cwnd; /* cwnd right before starting loss recovery */ u32 prr_delivered; /* Number of newly delivered packets to * receiver in Recovery. */ u32 prr_out; /* Total number of pkts sent during Recovery. */ diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index fde983f..c2b1744 100644 --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -456,7 +456,7 @@ 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); + return max(tp->snd_cwnd, tp->prior_cwnd); } EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd); diff --git a/net/ipv4/tcp_htcp.c b/net/ipv4/tcp_htcp.c index 3eb78cd..082d479 100644 --- a/net/ipv4/tcp_htcp.c +++ b/net/ipv4/tcp_htcp.c @@ -66,7 +66,6 @@ static inline void htcp_reset(struct htcp *ca) static u32 htcp_cwnd_undo(struct sock *sk) { - const struct tcp_sock *tp = tcp_sk(sk); struct htcp *ca = inet_csk_ca(sk); if (ca->undo_last_cong) { @@ -76,7 +75,7 @@ static u32 htcp_cwnd_undo(struct sock *sk) ca->undo_last_cong = 0; } - return max(tp->snd_cwnd, (tp->snd_ssthresh << 7) / ca->beta); + return tcp_reno_undo_cwnd(sk); } static inline void measure_rtt(struct sock *sk, u32 srtt) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 99cdf4c..842ed75 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -1950,6 +1950,7 @@ void tcp_enter_loss(struct sock *sk) !after(tp->high_seq, tp->snd_una) || (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) { tp->prior_ssthresh = tcp_current_ssthresh(sk); + tp->prior_cwnd = tp->snd_cwnd; tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); tcp_ca_event(sk, CA_EVENT_LOSS); tcp_init_undo(tp); -- 2.7.4