netdev - Re: WARN trace - skb_warn_bad_offload - vxlan - large udp packet

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Date:	Thu, 7 Jan 2016 08:27:42 +0100
From:	Michal Kubecek <mkubecek@...e.cz>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	"Nelson, Shannon" <shannon.nelson@...el.com>,
	Tom Herbert <tom@...bertland.com>,
	Jesse Gross <jesse@...ira.com>, Jiri Benc <jbenc@...hat.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: WARN trace - skb_warn_bad_offload - vxlan - large udp packet -
 udp checksum disabled

On Thu, Jan 07, 2016 at 07:46:40AM +0100, Michal Kubecek wrote:
> On Thu, Jan 07, 2016 at 03:36:27AM +0100, Hannes Frederic Sowa wrote:
> > On 15.12.2015 02:35, Nelson, Shannon wrote:
> > >Using a slightly modified version of udpspam (see diff below -
> > >hopefully not mangled by corporate email servers), where I set the
> > >SO_NO_CHECK socket option and can specify a large buffer size, I can
> > >reliably get the following WARN trace.  I have reproduced this on
> > >both ixgbe and i40e drivers using "udpspam-no-check <target-ip>
> > >6000".
> > >
> > >It looks to me like this is in the Tx path before we get to the
> > >actual NIC drivers, but I may be wrong.
> > 
> > Does UFO offloading on the tunnel interface fix this error?
> > 
> > ethtool -K vxlan ufo off
> > 
> > If yes we can't feed SO_NO_CHECK udp packets into UFO as gso/ufo
> > requires CHECKSUM_PARTIAL (or add some more logic into the skb or
> > query socket status from skb_gso_segment).
> 
> I believe you are right. This sounds like the issue addressed by commit
> acf8dd0a9d0b ("udp: only allow UFO for packets from SOCK_DGRAM sockets")
> except for a regular SOCK_DGRAM socket with SO_NO_CHECK option. If so,
> changing both instances of the check
> 
> 	    (sk->sk_type == SOCK_DGRAM)
> 
> added by this commit to
> 
> 	    (sk->sk_type == SOCK_DGRAM) && !sk->sk_no_check_tx
> 
> should fix the problem (and it should be done even if the issue reported
> here is caused by something else).

Correction: the IPv6 case will need "!udp_get_no_check6_tx(sk)" instead.

Michal Kubecek

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