netdev - Re: [RFC PATCH] net: ip_finish_output_gso: Attempt gso

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Date:   Mon, 22 Aug 2016 16:05:34 +0300
From:   Shmulik Ladkani <shmulik.ladkani@...il.com>
To:     Florian Westphal <fw@...len.de>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: 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@...len.de wrote:
> > 
> >  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@...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.