From b20a3fa30a281b52b2576b509efbe5cd47a5a79b Mon Sep 17 00:00:00 2001 From: Yuchung Cheng Date: Thu, 9 Jul 2015 13:16:31 -0700 Subject: [PATCH] tcp: update congestion state first before raising cwnd The congestion state and cwnd can be updated in the wrong order. For example, upon receiving a dubious ACK, we incorrectly raise the cwnd first (tcp_may_raise_cwnd()/tcp_cong_avoid()) because the state is still Open, then enter recovery state to reduce cwnd. For another example, if the ACK indicates spurious timeout or retransmits, we first revert the cwnd reduction and congestion state back to Open state. But we don't raise the cwnd even though the ACK does not indicate any congestion. To fix this problem we should first call tcp_fastretrans_alert() to process the dubious ACK and update the congestion state, then call tcp_may_raise_cwnd() that raises cwnd based on the current state. Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: Eric Dumazet Signed-off-by: Nandita Dukkipati Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 7f4a8d5f6eb0..1578fc2a6f39 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -3568,10 +3568,6 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) &sack_state); acked -= tp->packets_out; - /* Advance cwnd if state allows */ - if (tcp_may_raise_cwnd(sk, flag)) - tcp_cong_avoid(sk, ack, acked); - if (tcp_ack_is_dubious(sk, flag)) { is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP)); tcp_fastretrans_alert(sk, acked, prior_unsacked, @@ -3580,6 +3576,10 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) if (tp->tlp_high_seq) tcp_process_tlp_ack(sk, ack, flag); + /* Advance cwnd if state allows */ + if (tcp_may_raise_cwnd(sk, flag)) + tcp_cong_avoid(sk, ack, acked); + if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) { struct dst_entry *dst = __sk_dst_get(sk); if (dst) -- 2.20.1