On Mon, Nov 28, 2016 at 03:54:59PM -0500, David Miller wrote:
> From: Alex Sidorenko <alexandre.sidore...@hpe.com>
> Date: Mon, 28 Nov 2016 15:49:26 -0500
>
> > Now the question is whether is is OK to have icsk->icsk_ack.rcv_mss
> > larger than MTU.
>
> It absolutely is not OK.
>
Would it make sense to add a pr_warn_once() and perhaps even clamp it
down to known/saner MSS?
> If VMWare wants to receive large frames for batching purposes it must
> use GRO or similar to achieve that, not just send vanilla frames into
> the stack which are larger than the device MTU.
>
It's not the first report I've seen on this type of issue. IBM also had
this issue recently while not being able to send the gso_size from tx
side to rx, and the warning probably could have saved quite some
debugging time.
Something like (but with a better msg, for sure):
--8<--
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a27b9c0e27c0..3a59cffae3fa 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -144,7 +144,9 @@ static void tcp_measure_rcv_mss(struct sock *sk, const
struct sk_buff *skb)
*/
len = skb_shinfo(skb)->gso_size ? : skb->len;
if (len >= icsk->icsk_ack.rcv_mss) {
- icsk->icsk_ack.rcv_mss = len;
+ icsk->icsk_ack.rcv_mss = max(len, tcp_sk(sk)->advmss);
+ if (icsk->icsk_ack.rcv_mss != len)
+ pr_warn_once("Your driver is likely doing bad rx
acceleration.\n");
} else {
/* Otherwise, we make more careful check taking into account,
* that SACKs block is variable.
