From patchwork Sun Feb 3 19:13:05 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Subject: tcp: frto should not set snd_cwnd to 0 Date: Sun, 03 Feb 2013 09:13:05 -0000 From: Eric Dumazet X-Patchwork-Id: 217797 Message-Id: <1359918785.30177.111.camel@edumazet-glaptop> To: Neal Cardwell , Ilpo =?ISO-8859-1?Q?J=E4rvinen?= Cc: Pasi =?ISO-8859-1?Q?K=E4rkk=E4inen?= , David Miller , Hannes Frederic Sowa , Stephen Hemminger , Netdev , Yuchung Cheng From: Eric Dumazet Commit 9dc274151a548 (tcp: fix ABC in tcp_slow_start()) uncovered a bug in FRTO code : tcp_process_frto() is setting snd_cwnd to 0 if the number of in flight packets is 0. As Neal pointed out, if no packet is in flight we lost our chance to disambiguate whether a loss timeout was spurious. We should assume it was a proper loss. Reported-by: Pasi Kärkkäinen Signed-off-by: Neal Cardwell Signed-off-by: Eric Dumazet Cc: Ilpo Järvinen Cc: Yuchung Cheng --- net/ipv4/tcp_input.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 8aca4ee..680c422 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -3484,7 +3484,8 @@ static bool tcp_process_frto(struct sock *sk, int flag) ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED))) tp->undo_marker = 0; - if (!before(tp->snd_una, tp->frto_highmark)) { + if (!before(tp->snd_una, tp->frto_highmark) || + !tcp_packets_in_flight(tp)) { tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag); return true; }