On 17/02/16 20:08, Steffen Klassert wrote:
> On Wed, Feb 10, 2016 at 01:50:20AM +0000, Mark McKinstry wrote:
>>> So this version is slightly modified to cover the IPv4 case in addition to
>>> the IPv6 case. With this patch I was able to run netperf over either an
>>> IPv4 or IPv6 address routed over the ip6_vti tunnel.
>> We have the same issue. When we do a local ping to a remote device over
>> a v4 vti tunnel and an intermediate device has a low mtu, pmtu
>> discovery reduces the route's pmtu, and ping fails because it does not
>> handle the local error message generated by xfrm4_tunnel_check_size().
>> Your patch fixes our issue for v6 vti tunnels, but the issue still
>> exists for v4 tunnels. Is there any particular reason this patch was
>> not delivered for v4 tunnels too - i.e. in vti_xmit()?
> I don't remember why we fixed it just for ipv6, we probably need
> a similar patch for ipv4.
>
> Does the patch below help (compile tested only)?
>
> Subject: [PATCH] vti: Add pmtu handling to vti_xmit.
>
> We currently rely on the PMTU discovery of xfrm.
> However if a packet is localy sent, the PMTU mechanism
> of xfrm tries to to local socket notification what
> might not work for applications like ping that don't
> check for this. So add pmtu handling to vti_xmit to
> report MTU changes immediately.
>
> Signed-off-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
> ---
> net/ipv4/ip_vti.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
> index 5cf10b7..6862305 100644
> --- a/net/ipv4/ip_vti.c
> +++ b/net/ipv4/ip_vti.c
> @@ -156,6 +156,7 @@ static netdev_tx_t vti_xmit(struct sk_buff *skb, struct net_device *dev,
> struct dst_entry *dst = skb_dst(skb);
> struct net_device *tdev; /* Device to other host */
> int err;
> + int mtu;
>
> if (!dst) {
> dev->stats.tx_carrier_errors++;
> @@ -196,6 +197,18 @@ static netdev_tx_t vti_xmit(struct sk_buff *skb, struct net_device *dev,
> skb_dst_set(skb, dst);
> skb->dev = skb_dst(skb)->dev;
>
> + mtu = dst_mtu(dst);
> + if (!skb->ignore_df && skb->len > mtu) {
> + skb_dst(skb)->ops->update_pmtu(dst, NULL, skb, mtu);
> + if (skb->protocol == htons(ETH_P_IP))
> + icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
> + htonl(mtu));
> + else
> + icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
> +
> + return -EMSGSIZE;
> + }
> +
> err = dst_output(tunnel->net, skb->sk, skb);
> if (net_xmit_eval(err) == 0)
> err = skb->len;
This patch fixes our issue, thanks. In our scenario the tunnel path MTU
now gets updated so that subsequent large packets sent over the tunnel
get fragmented correctly.--
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