From c7d9d6a185a7ea383b719b79c428d34ec1470275 Mon Sep 17 00:00:00 2001 From: Yuchung Cheng Date: Wed, 29 May 2013 14:20:14 +0000 Subject: [PATCH] tcp: undo on DSACK during recovery If the receiver supports DSACK, sender can detect false recoveries and revert cwnd reductions triggered by either severe network reordering or concurrent reordering and loss event. Signed-off-by: Yuchung Cheng Acked-by: Neal Cardwell Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index c35b22751982..907311c9a012 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2315,7 +2315,7 @@ static bool tcp_try_undo_recovery(struct sock *sk) } /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */ -static void tcp_try_undo_dsack(struct sock *sk) +static bool tcp_try_undo_dsack(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); @@ -2323,7 +2323,9 @@ static void tcp_try_undo_dsack(struct sock *sk) DBGUNDO(sk, "D-SACK"); tcp_undo_cwnd_reduction(sk, false); NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO); + return true; } + return false; } /* We can clear retrans_stamp when there are no retransmissions in the @@ -2751,6 +2753,10 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked, do_lost = tcp_is_reno(tp) || tcp_fackets_out(tp) > tp->reordering; } + if (tcp_try_undo_dsack(sk)) { + tcp_try_keep_open(sk); + return; + } break; case TCP_CA_Loss: tcp_process_loss(sk, flag, is_dupack);