From: Jiri Olsa <jolsa@redhat.com>
Date: Wed, 8 Apr 2009 15:57:02 +0200
Subject: [net] fixed tcp_ack to properly clear ->icsk_probes_out
Message-id: 20090408135702.GA32047@jolsa.englab.brq.redhat.com
O-Subject: [RHEL5.5 PATCH] BZ494427 net - fixed tcp_ack() to properly clear ->icsk_probes_out
Bugzilla: 494427
RH-Acked-by: Jiri Pirko <jpirko@redhat.com>
RH-Acked-by: Thomas Graf <tgraf@redhat.com>
RH-Acked-by: David Miller <davem@redhat.com>

Bugzilla: 494427
https://bugzilla.redhat.com/show_bug.cgi?id=494427

Description:
============

This is based upon an excellent bug report from Eric Dumazet in
"git.kernel.org"

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=4b53fb67e385b856a991d402096379dab462170a

tcp_ack() should clear ->icsk_probes_out even if there are packets
outstanding.  Otherwise if we get a sequence of ACKs while we do have
packets outstanding over and over again, we'll never clear the
probes_out value and eventually think the connection is too sick and
we'll reset it.

Upstream status:
================

commit 4b53fb67e385b856a991d402096379dab462170a
Author: David S. Miller <davem@davemloft.net>

Test status of the patch:
=========================

succesfully reproduced/tested with the test program from the upstream patch
- compiled/attached to the bug (x86_64 arch)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 46b12a6..a5cb1fd 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2558,6 +2558,7 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
 	 * log. Something worked...
 	 */
 	sk->sk_err_soft = 0;
+	icsk->icsk_probes_out = 0;
 	tp->rcv_tstamp = tcp_time_stamp;
 	prior_packets = tp->packets_out;
 	if (!prior_packets)
@@ -2587,8 +2588,6 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
 	return 1;
 
 no_queue:
-	icsk->icsk_probes_out = 0;
-
 	/* If this ack opens up a zero window, clear backoff.  It was
 	 * being used to time the probes, and is probably far higher than
 	 * it needs to be for normal retransmission.