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

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Message-ID: <20160106182354.000044e9@unknown>
Date:	Wed, 6 Jan 2016 18:23:54 -0800
From:	Jesse Brandeburg <jesse.brandeburg@...el.com>
To:	"Nelson, Shannon" <shannon.nelson@...el.com>
Cc:	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>, jesse.brandeburg@...el.com
Subject: Re: WARN trace - skb_warn_bad_offload - vxlan - large udp packet -
 udp checksum disabled

On Tue, 15 Dec 2015 01:35:27 +0000
"Nelson, Shannon" <shannon.nelson@...el.com> 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.
> 
> 
> [ 1757.644324] ------------[ cut here ]------------
> [ 1757.644333] WARNING: CPU: 22 PID: 5537 at net/core/dev.c:2423 skb_warn_bad_offload+0x104/0x111()

Was anyone able to take a look at this?  There is a pretty clear
reproducer in the original mail.

I know SO_NO_CHECK is a lightly used option, but it does exist and we
found a userspace program that tries to use it.
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