From 6adb4f733e9996b4fd68a6db50dd51bd2463ccac Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@helsinki.fi>
Date: Mon, 7 Apr 2008 22:33:57 -0700
Subject: [TCP]: Don't allow FRTO to take place while MTU is being probed
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MTU probe can cause some remedies for FRTO because the normal
packet ordering may be violated allowing FRTO to make a wrong
decision (it might not be that serious threat for anything
though). Thus it's safer to not run FRTO while MTU probe is
underway.

It seems that the basic FRTO variant should also look for an
skb at probe_seq.start to check if that's retransmitted one
but I didn't implement it now (plain seqno in window check
isn't robust against wraparounds).

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
 net/ipv4/tcp_input.c | 5 +++++
 1 file changed, 5 insertions(+)

(limited to 'net')

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index b4812c3..5119856 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1691,11 +1691,16 @@ static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
 int tcp_use_frto(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
+	const struct inet_connection_sock *icsk = inet_csk(sk);
 	struct sk_buff *skb;
 
 	if (!sysctl_tcp_frto)
 		return 0;
 
+	/* MTU probe and F-RTO won't really play nicely along currently */
+	if (icsk->icsk_mtup.probe_size)
+		return 0;
+
 	if (IsSackFrto())
 		return 1;
 
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