netdev - Re: 答复: 答复: 答复: [PATCH] set fake_rtable's dst to NULL to avoid kernel Oops.

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Date:	Sat, 31 Mar 2012 07:41:26 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Peter Huang (Peng)" <peter.huangpeng@...wei.com>
Cc:	linux-kernel@...r.kernel.org, harry.majun@...wei.com,
	zhoukang7@...wei.com, 'netdev' <netdev@...r.kernel.org>
Subject: Re: 答复: 答复: 答复:
 [PATCH] set fake_rtable's dst to NULL to avoid kernel Oops.

On Sat, 2012-03-31 at 09:26 +0800, Peter Huang (Peng) wrote:
> > > >Check net/bridge/br_netfilter.c and commits e688a6048076 (net: introduce
> > > >DST_NOPEER dst flag )  4adf0af6818f3ea5 (bridge: send correct MTU value
> > > >in PMTU (revised))
> 
> Hi, Eric
> 
> I confirmed the patch contents again.
> For our case, NF_INET_PRE_ROUTING is involved, not NF_BR_LOCAL_IN. 
> It seems pre-routing is not included in the patch you mentioned.
> BTW, our pkts are all ipv6 DHCP pkts(with MAC 33 33 00 01 00 02).
> 
> We verified the patch bellow, and this works fine, no WARN_ON happened. 

Hi Peter

I claim that your patch is not the good one and you need to refine it.

First, code is not needed if CONFIG_BRIDGE_NETFILTER is not set.

In fact, if CONFIG_BRIDGE_NETFILTER is not set, compilation will fail
since fake_rtable doesnt exist in "struct net_bridge", so you fix a bug
and introduce a new one.

  CC [M]  net/bridge/br_forward.o
net/bridge/br_forward.c: In function ‘__br_forward’:
net/bridge/br_forward.c:94: error: ‘struct sk_buff’ has no member named ‘_skb_dst’
net/bridge/br_forward.c:94: error: ‘struct net_bridge’ has no member named ‘fake_rtable’
make[1]: *** [net/bridge/br_forward.o] Error 1
make: *** [_module_net/bridge] Error 2

Then, the test is using obsolete dst internals and cast that should not
be in a C file. : 

if (skb->_skb_dst == (unsigned long)&to->br->fake_rtable)

So I suggested you take a look at net/bridge/br_netfilter.c code to see
how this can be done properly. Maybe you need to add a helper in an
include file to make this proper.

I hope this is now clear to you, because your initial patch cannot be
applied as is. If you want full credit for this work, you must go a step
forward, or else another guy will finish the job.

Thanks

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