netdev - Re: skb_shinfo(skb)->nr_frags > 0 while skb_is

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Date:	Wed, 7 Oct 2009 03:04:20 -0600
From:	John Wright <john.wright@...com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	netdev@...r.kernel.org, Michael Chan <mchan@...adcom.com>,
	Bob Montgomery <bob.montgomery@...com>
Subject: Re: skb_shinfo(skb)->nr_frags > 0 while skb_is_gso(skb) == 0?

Hi Stephen,

On Tue, Oct 06, 2009 at 06:21:31PM -0700, Stephen Hemminger wrote:
> On Tue, 6 Oct 2009 19:03:15 -0600
> John Wright <john.wright@...com> wrote:
> > Bob Montgomery and I are debugging an OOPS in the bnx2 driver.  The
> > driver OOPSes in bnx2_tx_int(), getting a NULL pointer dereference when
> > checking if the skb is GSO.  (This is on 2.6.29, before is_gso was
> > cached in the tx_buf (commit d62fda08), but bear with me - while kernels
> > with that commit might not crash in the same place, I think we have
> > discovered a bug that would manifest itself another way.)
> > 
> > So, first, a question for someone who knows more about sk_buff's than I:
> > is it reasonable/legal for an skb for which skb_is_gso(skb) == 0 to also
> > have skb_shinfo(skb)->nr_frags > 0?
> 
> Yes, if driver support Scatter/Gather and Checksum offload,
> TCP (especially splice) will hand fragmented frames to device.

Is there a good way to generate lots of these types of packets?  Is
disabling tso and gso with ethtool and sendmsg()ing big chunks of data
enough?

-- 
+----------------------------------------------------------+
| John Wright <john.wright@...com>                         |
| HP Mission Critical OS Enablement & Solution Test (MOST) |
+----------------------------------------------------------+
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