Re: [RFC PATCH] net: ip_finish_output_gso: Attempt gso_size clamping if segments exceed mtu

Hi,

On Mon, 22 Aug 2016 14:58:42 +0200, fw@strlen.de wrote:

quoted

 Florian, in fe6cc55f you described a BUG due to gso_size decrease.
 I've tested both bridged and routed cases, but in my setups failed to
 hit the issue; Appreciate if you can provide some hints.

Still get the BUG, I applied this patch on top of net-next.

On hypervisor:
10.0.0.2 via 192.168.7.10 dev tap0 mtu lock 1500
ssh root@10.0.0.2 'cat > /dev/null' < /dev/zero

On vm1 (which dies instantly, see below):
eth0 mtu 1500 (192.168.7.10)
eth1 mtu 1280 (10.0.0.1)

On vm2
eth0 mtu 1280 (10.0.0.2)

Normal ipv4 routing via vm1, no iptables etc. present, so

we have  hypervisor 1500 -> 1500 VM1 1280 -> 1280 VM2

Turning off gro avoids this problem.

Thanks Florian, will dive into this.