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: Jiri Slaby <jslaby@suse.cz>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 4c0e55f14f2ea8e9139ae525cccca4c2a9645bda..b4435ae4c48553d58e8644f3bf9321ab14228d06 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1871,7 +1871,7 @@ 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))))
@@ -1908,7 +1908,7 @@ 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,