Re: [REGRESSION, bisect]cxgb4 port failure with TSO traffic after commit 10d3be569243def8("tcp-tso: do not split TSO packets at retransmit time")

On Mon, 2016-06-27 at 12:50 +0200, Eric Dumazet wrote:

On Mon, 2016-06-27 at 15:24 +0530, Arjun V wrote:

quoted

Applied your patch.
The above debug print is not getting invoked, when skb->len is greater than 65536.

Interesting.

It looks like we might have a bug in tcp_shift_skb_data() not respecting
sk->sk_gso_max_size at all ...

Note that this also means TCP receiver misbehaves and force us to SACK
reneging.

Patch would be :

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 8bd9911fdd16..3587efe22864 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c

@@ -2784,6 +2784,10 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
 		segs = tp->snd_cwnd - tcp_packets_in_flight(tp);
 		if (segs <= 0)
 			return;
+		/* In case tcp_shift_skb_data() have aggregated large skbs,
+		 * we need to make sure not sending too big TSO packets.
+		 */
+		segs = min_t(int, segs, tp->gso_segs);
 
 		if (fwd_rexmitting) {
 begin_fwd: