From da34ac7626b571d262f92b93f11eb32dd58d9c4e Mon Sep 17 00:00:00 2001 From: Yuchung Cheng Date: Mon, 18 May 2015 12:31:44 -0700 Subject: [PATCH] tcp: only undo on partial ACKs in CA_Loss Undo based on TCP timestamps should only happen on ACKs that advance SND_UNA, according to the Eifel algorithm in RFC 3522: Section 3.2: (4) If the value of the Timestamp Echo Reply field of the acceptable ACK's Timestamps option is smaller than the value of RetransmitTS, then proceed to step (5), Section Terminology: We use the term 'acceptable ACK' as defined in [RFC793]. That is an ACK that acknowledges previously unacknowledged data. This is because upon receiving an out-of-order packet, the receiver returns the last timestamp that advances RCV_NXT, not the current timestamp of the packet in the DUPACK. Without checking the flag, the DUPACK will cause tcp_packet_delayed() to return true and tcp_try_undo_loss() will revert cwnd reduction. Note that we check the condition in CA_Recovery already by only calling tcp_try_undo_partial() if FLAG_SND_UNA_ADVANCED is set or tcp_try_undo_recovery() if snd_una crosses high_seq. Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index bc790ea9960f..9faf775a8c4a 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2698,11 +2698,16 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack) struct tcp_sock *tp = tcp_sk(sk); bool recovered = !before(tp->snd_una, tp->high_seq); + if ((flag & FLAG_SND_UNA_ADVANCED) && + tcp_try_undo_loss(sk, false)) + return; + if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */ /* Step 3.b. A timeout is spurious if not all data are * lost, i.e., never-retransmitted data are (s)acked. */ - if (tcp_try_undo_loss(sk, flag & FLAG_ORIG_SACK_ACKED)) + if ((flag & FLAG_ORIG_SACK_ACKED) && + tcp_try_undo_loss(sk, true)) return; if (after(tp->snd_nxt, tp->high_seq) && @@ -2732,8 +2737,6 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack) else if (flag & FLAG_SND_UNA_ADVANCED) tcp_reset_reno_sack(tp); } - if (tcp_try_undo_loss(sk, false)) - return; tcp_xmit_retransmit_queue(sk); } -- 2.20.1