From: Danny Feng <dfeng@redhat.com>
Date: Thu, 25 Jun 2009 22:40:44 -0400
Subject: [net] tcp: do not use TSO/GSO when there is urgent data
Message-id: 20090626024101.5124.50043.sendpatchset@dhcp-65-180.nay.redhat.com
O-Subject: [PATCH RHEL5.5] tcp: Do not use TSO/GSO when there is urgent data
Bugzilla: 502572
RH-Acked-by: David Miller <davem@redhat.com>
RH-Acked-by: Rik van Riel <riel@redhat.com>

RHBZ#:
======
https://bugzilla.redhat.com/show_bug.cgi?id=502572

Description:
===========
telnet login to RHEL5 system, do a "cat <filename>" and press CTRL+C.
This command stop the output on display succesfully.
But on the 2nd attempt, cat <filename> the text scroll stop responding
when the text scroll reach a position where I hit CTRL+C before.

NOTE:
1. This can only be reproduce by a special telnet connection:
       PC =>(ssh) RHEL 4/5 =>(telnet) RHEL 5
2. This can only be reproduced on some specific ethernet card:
       Broadcom NetXtreme II BCM5708
       Intel 82541GI
       (Maybe some other I didn't find)

RHEL Version Found:
================
RHEL 5.5

kABI Status:
============
No symbols were harmed.

Brew:
=====
Built on all platforms.
http://brewweb.devel.redhat.com/brew/taskinfo?taskID=1861295

Upstream Status:
================
The original patch, applied upstream is this one:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=33cf71cee14743185305c61625c4544885055733

It is a very simple change, so the patch was not hard to port.

Test Status:
============
Test has been done on following RHTS machines:
dell-pesc1425-01.rhts.bos.redhat.com (Intel 82541GI ethernet card)
ibm-e326m.rhts.bos.redhat.com (Broadcom NetXtreme II BCM5708 ethernet card)

The proposed patch can fix this BZ.

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 1b4622b..05dec8a 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -513,7 +513,10 @@ static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
 
 static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb, unsigned int mss_now)
 {
-	if (skb->len <= mss_now || !sk_can_gso(sk)) {
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	if (skb->len <= mss_now || !sk_can_gso(sk) ||
+	    tp->urg_mode) {
 		/* Avoid the costly divide in the normal
 		 * non-TSO case.
 		 */
@@ -913,8 +916,10 @@ static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp, struct sk_buff *sk
 static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb, unsigned int mss_now)
 {
 	int tso_segs = tcp_skb_pcount(skb);
+	struct tcp_sock *tp = tcp_sk(sk);
 
-	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
+	if (!tso_segs || (tso_segs > 1 && (tcp_skb_mss(skb) != mss_now ||
+			tp->urg_mode))) {
 		tcp_set_skb_tso_segs(sk, skb, mss_now);
 		tso_segs = tcp_skb_pcount(skb);
 	}