tcp: Do not apply TSO segment limit to non-TSO packets

[ Upstream commit 843925f33fcc293d80acf2c5c8a78adf3344d49b ]

Thomas Jarosch reported IPsec TCP stalls when a PMTU event occurs.

In fact the problem was completely unrelated to IPsec.  The bug is
also reproducible if you just disable TSO/GSO.

The problem is that when the MSS goes down, existing queued packet
on the TX queue that have not been transmitted yet all look like
TSO packets and get treated as such.

This then triggers a bug where tcp_mss_split_point tells us to
generate a zero-sized packet on the TX queue.  Once that happens
we're screwed because the zero-sized packet can never be removed
by ACKs.

Fixes: 1485348d242 ("tcp: Apply device TSO segment limit earlier")
Reported-by: Thomas Jarosch <thomas.jarosch@intra2net.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Cheers,
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 11ef25c9cf43200548f5a75760adb2f509575124..923146c4f007699d563fa71914808e4d2a1b3965 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1862,7 +1862,7 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
                if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
                        break;
 
-               if (tso_segs == 1) {
+               if (tso_segs == 1 || !sk->sk_gso_max_segs) {
                        if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
                                                     (tcp_skb_is_last(sk, skb) ?
                                                      nonagle : TCP_NAGLE_PUSH))))
@@ -1899,7 +1899,7 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
                }
 
                limit = mss_now;
-               if (tso_segs > 1 && !tcp_urg_mode(tp))
+               if (tso_segs > 1 && sk->sk_gso_max_segs && !tcp_urg_mode(tp))
                        limit = tcp_mss_split_point(sk, skb, mss_now,
                                                    min_t(unsigned int,
                                                          cwnd_quota,