On 10/25/2016 07:09 PM, Jon Maxwell wrote:
> We recently encountered a bug where a few customers using ibmveth on the
> same LPAR hit an issue where a TCP session hung when large receive was
> enabled. Closer analysis revealed that the session was stuck because the
> one side was advertising a zero window repeatedly.
>
> We narrowed this down to the fact the ibmveth driver did not set gso_size
> which is translated by TCP into the MSS later up the stack. The MSS is
> used to calculate the TCP window size and as that was abnormally large,
> it was calculating a zero window, even although the sockets receive buffer
> was completely empty.
>
> We were able to reproduce this and worked with IBM to fix this. Thanks Tom
> and Marcelo for all your help and review on this.
>
> The patch fixes both our internal reproduction tests and our customers tests.
>
> Signed-off-by: Jon Maxwell <jmaxwel...@gmail.com>
Thanks, Jon.
Acked-by: Thomas Falcon <tlfal...@linux.vnet.ibm.com>
> ---
> drivers/net/ethernet/ibm/ibmveth.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/drivers/net/ethernet/ibm/ibmveth.c
> b/drivers/net/ethernet/ibm/ibmveth.c
> index 29c05d0..c51717e 100644
> --- a/drivers/net/ethernet/ibm/ibmveth.c
> +++ b/drivers/net/ethernet/ibm/ibmveth.c
> @@ -1182,6 +1182,8 @@ static int ibmveth_poll(struct napi_struct *napi, int
> budget)
> int frames_processed = 0;
> unsigned long lpar_rc;
> struct iphdr *iph;
> + bool large_packet = 0;
> + u16 hdr_len = ETH_HLEN + sizeof(struct tcphdr);
>
> restart_poll:
> while (frames_processed < budget) {
> @@ -1236,10 +1238,28 @@ static int ibmveth_poll(struct napi_struct *napi, int
> budget)
> iph->check = 0;
> iph->check =
> ip_fast_csum((unsigned char *)iph, iph->ihl);
> adapter->rx_large_packets++;
> + large_packet = 1;
> }
> }
> }
>
> + if (skb->len > netdev->mtu) {
> + iph = (struct iphdr *)skb->data;
> + if (be16_to_cpu(skb->protocol) == ETH_P_IP &&
> + iph->protocol == IPPROTO_TCP) {
> + hdr_len += sizeof(struct iphdr);
> + skb_shinfo(skb)->gso_type =
> SKB_GSO_TCPV4;
> + skb_shinfo(skb)->gso_size = netdev->mtu
> - hdr_len;
> + } else if (be16_to_cpu(skb->protocol) ==
> ETH_P_IPV6 &&
> + iph->protocol == IPPROTO_TCP) {
> + hdr_len += sizeof(struct ipv6hdr);
> + skb_shinfo(skb)->gso_type =
> SKB_GSO_TCPV6;
> + skb_shinfo(skb)->gso_size = netdev->mtu
> - hdr_len;
> + }
> + if (!large_packet)
> + adapter->rx_large_packets++;
> + }
> +
> napi_gro_receive(napi, skb); /* send it up */
>
> netdev->stats.rx_packets++;
