netdev - Re: __pskb_pull_tail oops from 2.6.35

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Date:	Wed, 28 Sep 2011 10:30:00 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Dave Jones <davej@...hat.com>, David Miller <davem@...emloft.net>,
	netdev@...r.kernel.org
Subject: Re: __pskb_pull_tail oops from 2.6.35


	Hello,

On Tue, 27 Sep 2011, Eric Dumazet wrote:

> Le mardi 27 septembre 2011 à 16:24 -0400, Dave Jones a écrit :
> > On Tue, Sep 27, 2011 at 04:18:48PM -0400, David Miller wrote:
> >  > From: Dave Jones <davej@...hat.com>
> >  > Date: Tue, 27 Sep 2011 16:15:00 -0400
> >  > 
> >  > > It looks like it died in put_page..
> >  > > 
> >  > > <1>[  262.574991] IP: [<ffffffff810dca57>] put_page+0x10/0x7c
> >  > > 
> >  > > which is only called in one place..
> >  > > 
> >  > > 1267         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
> >  > > 1268                 if (skb_shinfo(skb)->frags[i].size <= eat) {
> >  > > 1269                         put_page(skb_shinfo(skb)->frags[i].page);
> >  > > 1270                         eat -= skb_shinfo(skb)->frags[i].size;
> >  > > 1271                 } else {
> >  > 
> >  > That's a pretty serious corruption, all frag array entries from 0 to
> >  > nr_frags should have valid, non-NULL page pointers.
> >  > 
> >  > Maybe a LRO/GRO bug?  There were a couple of those.
> > 
> > I'll see if I can talk him into trying a self-built kernel, as we're not
> > rebasing f14 at this point in its life-cycle. If it turns out to still affect
> > 3.x, I'll bring it up again.
> > 
> 
> This could be a struct skb_shared_info -> nr_frags corruption
> 
> (Something was overflowing skb head and overflowing very beginning of
> skb_shared_info in rare circumstances)
> 
> We had such bug in the past, I cant remember details right now.

	I remember for similar problem that was fixed
recently (IPVS+nf_reinject), oops is here:

http://marc.info/?l=linux-virtual-server&m=131098073717449&w=2

	Oops points to put_page but not sure for the call trace.
Code auditing pointed out to be a double kfree_skb issue. Still,
it was never confirmed by the original reporter. May be
problem with double kfree_skb is easier to track in all
modules that play with the packet.

Regards

--
Julian Anastasov <ja@....bg>