[ 3.5.y.z extended stable ] Patch "tcp: xps: fix reordering issues" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    tcp: xps: fix reordering issues

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From ba0835b1a9d31eed3970fe4552b28884c95e0b6e Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet at google.com>
Date: Thu, 23 May 2013 07:44:20 +0000
Subject: [PATCH] tcp: xps: fix reordering issues

commit 547669d483e5783d722772af1483fa474da7caf9 upstream.

commit 3853b5841c01a ("xps: Improvements in TX queue selection")
introduced ooo_okay flag, but the condition to set it is slightly wrong.

In our traces, we have seen ACK packets being received out of order,
and RST packets sent in response.

We should test if we have any packets still in host queue.

Signed-off-by: Eric Dumazet <edumazet at google.com>
Cc: Tom Herbert <therbert at google.com>
Cc: Yuchung Cheng <ycheng at google.com>
Cc: Neal Cardwell <ncardwell at google.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/ipv4/tcp_output.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ae12c92..4a1e840 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -836,11 +836,13 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
 							   &md5);
 	tcp_header_size = tcp_options_size + sizeof(struct tcphdr);

-	if (tcp_packets_in_flight(tp) == 0) {
+	if (tcp_packets_in_flight(tp) == 0)
 		tcp_ca_event(sk, CA_EVENT_TX_START);
-		skb->ooo_okay = 1;
-	} else
-		skb->ooo_okay = 0;
+
+	/* if no packet is in qdisc/device queue, then allow XPS to select
+	 * another queue.
+	 */
+	skb->ooo_okay = sk_wmem_alloc_get(sk) == 0;

 	skb_push(skb, tcp_header_size);
 	skb_reset_transport_header(skb);
--
1.8.1.2