From: Yuchung Cheng Date: Fri, 30 May 2014 22:25:59 +0000 (-0700) Subject: tcp: fix cwnd undo on DSACK in F-RTO X-Git-Tag: v4.9.8~6321^2~2 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=0cfa5c07d6d1d7f8e710fc671c5ba1ce85e09fa4;p=platform%2Fkernel%2Flinux-rpi3.git tcp: fix cwnd undo on DSACK in F-RTO This bug is discovered by an recent F-RTO issue on tcpm list https://www.ietf.org/mail-archive/web/tcpm/current/msg08794.html The bug is that currently F-RTO does not use DSACK to undo cwnd in certain cases: upon receiving an ACK after the RTO retransmission in F-RTO, and the ACK has DSACK indicating the retransmission is spurious, the sender only calls tcp_try_undo_loss() if some never retransmisted data is sacked (FLAG_ORIG_DATA_SACKED). The correct behavior is to unconditionally call tcp_try_undo_loss so the DSACK information is used properly to undo the cwnd reduction. Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: David S. Miller --- diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index d6b46eb..3a26b3b 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2684,13 +2684,12 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack) bool recovered = !before(tp->snd_una, tp->high_seq); if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */ - if (flag & FLAG_ORIG_SACK_ACKED) { - /* Step 3.b. A timeout is spurious if not all data are - * lost, i.e., never-retransmitted data are (s)acked. - */ - tcp_try_undo_loss(sk, true); + /* 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)) return; - } + if (after(tp->snd_nxt, tp->high_seq) && (flag & FLAG_DATA_SACKED || is_dupack)) { tp->frto = 0; /* Loss was real: 2nd part of step 3.a */