On Fri, Feb 03, 2017 at 05:24:06AM -0800, Eric Dumazet wrote:
> On Fri, 2017-02-03 at 09:54 -0200, Marcelo Ricardo Leitner wrote:
> > On Thu, Feb 02, 2017 at 05:59:24AM -0800, Eric Dumazet wrote:
> > > On Thu, 2017-02-02 at 05:31 -0800, Eric Dumazet wrote:
> > >
> > > > Anyway, I suspect the test is simply buggy ;)
> > > >
> > > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> > > > index
> > > > 41dcbd568cbe2403f2a9e659669afe462a42e228..5394a39fcce964a7fe7075b1531a8a1e05550a54
> > > > 100644
> > > > --- a/net/ipv4/tcp_input.c
> > > > +++ b/net/ipv4/tcp_input.c
> > > > @@ -164,7 +164,7 @@ static void tcp_measure_rcv_mss(struct sock *sk,
> > > > const struct sk_buff *skb)
> > > > if (len >= icsk->icsk_ack.rcv_mss) {
> > > > icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
> > > > tcp_sk(sk)->advmss);
> > > > - if (unlikely(icsk->icsk_ack.rcv_mss != len))
> > > > + if (unlikely(icsk->icsk_ack.rcv_mss != len &&
> > > > skb_is_gso(skb)))
> > > > tcp_gro_dev_warn(sk, skb);
> > > > } else {
> > > > /* Otherwise, we make more careful check taking into
> > > > account,
> > >
> > > This wont really help.
> > >
> > > Our tcp_sk(sk)->advmss can be lower than the MSS used by the remote
> > > peer.
> > >
> > > ip ro add .... advmss 512
> >
> > I don't follow. With a good driver, how can advmss be smaller than the
> > MSS used by the remote peer? Even with the route entry above, I get
> > segments just up to advmss, and no warning.
> >
>
> A TCP flow has two ends.
Indeed, though should be mostly about only one of them.
>
> Common MTU = 1500
>
> One can have advmss 500, the other one no advmss (or the standard 1460
> one)
Considering the rx side of peer A. Peer A advertises a given MSS to peer
B and should not receive any segment from peer B larger than so.
I'm failing to see how advmss can be smaller than the segment size just
received.
>
> So if we compare apple and orange, result might be shocking ;)
Yes heh just not seeing the mix here..
>
> If you want to reproduce this use the "ip ro add .... advmss 512" hint,
> and/or play with sysctl_tcp_mtu_probing
I tried the route with advmss, no luck so far.
Still digging..
Marcelo
