netdev - Re: gianfar.c null pointer deref in gfar_start

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Message-ID: <1312956061.2547.74.camel@edumazet-laptop>
Date:	Wed, 10 Aug 2011 08:01:01 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Robin Holt <holt@....com>
Cc:	Sandeep Gopalpet <Sandeep.Kumar@...escale.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: gianfar.c null pointer deref in gfar_start_xmit().

Le mardi 09 août 2011 à 08:06 -0500, Robin Holt a écrit :
> On Tue, Aug 09, 2011 at 09:10:13AM +0200, Eric Dumazet wrote:
> > Le mardi 09 août 2011 à 01:54 -0500, Robin Holt a écrit :
> > > On Tue, Aug 02, 2011 at 09:44:38PM -0500, Robin Holt wrote:
> > > > 
> > > > While using the v3.0 kernel on a Freescale P1010RDB with 3 minor patches
> > > > (None which affect gianfar.c), I get a NULL pointer deref at:
> > > > 
> > > > static int gfar_start_xmit(struct sk_buff *skb, struct net_device *dev)
> > > > {
> > > > ...
> > > > 	regs = tx_queue->grp->regs;
> > > > 
> > > > I put a BUG_ON(tx_queue->grp) just before this line and it did trip.
> > > > I have not looked at this any more than that.
> > > > 
> > > > Any suggestions would be welcome.   To reproduce, all I need to do is
> > > > a few sequences of pings.
> > > 
> > > I was able to reproduce this with the net-next-2.6 kernel as well.
> > > 
> > 
> > This driver incorrectly assumes a non dense txqueue array is possible
> > for a netdev, but its not true.
> > 
> > In the meantime, you could force it to use one tx_queue only.
> > 
> > tx_queues = (u32 *)of_get_property(np, "fsl,num_tx_queues", NULL);
> > num_tx_qs = tx_queues ? *tx_queues : 1;
> 
> I fixed up the .dts file and now it works.  I have not tested the RGMII
> interface yet so I do not know if that supports multiple queues.  I assume
> I could find it in the documentation.  What might I be looking for?
> 

What exact change did you in dts ?

Assuming your p1010rdb is single core powerpc, I fail to see why 8
queues should be enabled on NIC. It only increases number of interrupts
if multiple flows are in use, and memory footprint.



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