tcp: Do not use TSO/GSO when there is urgent data

This patch fixes http://bugzilla.kernel.org/show_bug.cgi?id=12014

Since most (if not all) implementations of TSO and even the in-kernel
software GSO do not update the urgent pointer when splitting a large
segment, it is necessary to turn off TSO/GSO for all outgoing traffic
with the URG pointer set.

Looking at tcp_current_mss (and the preceding comment) I even think
this was the original intention. However, this approach is insufficient,
because TSO/GSO is turned off only for newly created frames, not for
frames which were already pending at the arrival of a message with
MSG_OOB set. These frames were created when TSO/GSO was enabled,
so they may be large, and they will have the urgent pointer set
in tcp_transmit_skb().

With this patch, such large packets will be fragmented again before
going to the transmit routine.

As a side note, at least the following NICs are known to screw up
the urgent pointer in the TCP header when doing TSO:

	Intel 82566MM (PCI ID 8086:1049)
	Intel 82566DC (PCI ID 8086:104b)
	Intel 82541GI (PCI ID 8086:1076)
	Broadcom NetXtreme II BCM5708 (PCI ID 14e4:164c)

Signed-off-by: Petr Tesarik <ptesarik@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 2 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ba85d8831893..85b07eba1879 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -722,7 +722,8 @@ 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)) {
+        if (skb->len <= mss_now || !sk_can_gso(sk) ||
+            tcp_urg_mode(tcp_sk(sk))) {
                 /* Avoid the costly divide in the normal
                  * non-TSO case.
                  */
@@ -1163,7 +1164,9 @@ static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb,
 {
         int tso_segs = tcp_skb_pcount(skb);
 
-        if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
+        if (!tso_segs ||
+            (tso_segs > 1 && (tcp_skb_mss(skb) != mss_now ||
+                              tcp_urg_mode(tcp_sk(sk))))) {
                 tcp_set_skb_tso_segs(sk, skb, mss_now);
                 tso_segs = tcp_skb_pcount(skb);
         }