[PATCH 15/50] tcp: xps: fix reordering issues

[Luis Henriques]

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

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

From: Eric Dumazet <edumazet at google.com>

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