linux-kernel - [PATCH 68/81] tcp: fix for zero packets_in

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Message-Id: <1361299784-8830-69-git-send-email-herton.krzesinski@canonical.com>
Date:	Tue, 19 Feb 2013 15:49:31 -0300
From:	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>,
	"David S. Miller" <davem@...emloft.net>,
	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
Subject: [PATCH 68/81] tcp: fix for zero packets_in_flight was too broad

3.5.7.6 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@...sinki.fi>

commit 6731d2095bd4aef18027c72ef845ab1087c3ba63 upstream.

There are transients during normal FRTO procedure during which
the packets_in_flight can go to zero between write_queue state
updates and firing the resulting segments out. As FRTO processing
occurs during that window the check must be more precise to
not match "spuriously" :-). More specificly, e.g., when
packets_in_flight is zero but FLAG_DATA_ACKED is true the problematic
branch that set cwnd into zero would not be taken and new segments
might be sent out later.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Tested-by: Eric Dumazet <edumazet@...gle.com>
Acked-by: Neal Cardwell <ncardwell@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
---
 net/ipv4/tcp_input.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 6affa92..3b14d81 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3695,8 +3695,7 @@ 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) ||
-	    !tcp_packets_in_flight(tp)) {
+	if (!before(tp->snd_una, tp->frto_highmark)) {
 		tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
 		return true;
 	}
@@ -3716,6 +3715,11 @@ static bool tcp_process_frto(struct sock *sk, int flag)
 		}
 	} else {
 		if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
+			if (!tcp_packets_in_flight(tp)) {
+				tcp_enter_frto_loss(sk, 2, flag);
+				return true;
+			}
+
 			/* Prevent sending of new data. */
 			tp->snd_cwnd = min(tp->snd_cwnd,
 					   tcp_packets_in_flight(tp));
-- 
1.7.9.5

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