linux-kernel - Re: Linux 4.4.34

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Date:   Tue, 22 Nov 2016 18:08:45 +0000
From:   "Duyck, Alexander H" <alexander.h.duyck@...el.com>
To:     "maan@...bingen.mpg.de" <maan@...bingen.mpg.de>,
        "edumazet@...gle.com" <edumazet@...gle.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "willemb@...gle.com" <willemb@...gle.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "jslaby@...e.cz" <jslaby@...e.cz>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "yibyang@...co.com" <yibyang@...co.com>
Subject: Re: Linux 4.4.34

On Tue, 2016-11-22 at 19:06 +0100, Andre Noll wrote:
> On Tue, Nov 22, 09:56, Eric Dumazet wrote
> > 
> > > 
> > > > 
> > > > @@ -157,6 +157,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
> > > >                 memcpy(key_eth_addrs, &eth->h_dest, sizeof(*key_eth_addrs));
> > > >         }
> > > > 
> > > > +       barrier();
> > > >  again:
> > > >         switch (proto) {
> > > >         case htons(ETH_P_IP): {
> > > 
> > > This patch on top of v4.4.34 makes no difference: I'm still getting
> > > the panic in eth_type_trans().
> > > 
> > 
> > What compiler are you using exactly ?
> 
> gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3, as shipped with
> Ubuntu-12.04. I've also tried gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3)
> 4.8.4 from Ubuntu-14.04. No difference.
> 
> > 
> > diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
> > index 69e4463a4b1b..48791f372aa2 100644
> > --- a/net/core/flow_dissector.c
> > +++ b/net/core/flow_dissector.c
> > @@ -551,6 +551,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
> > 
> >         key_control->thoff = (u16)nhoff;
> >  out:
> > +       barrier();
> >         key_basic->n_proto = proto;
> >         key_basic->ip_proto = ip_proto;
> 
> No luck: Still the same panic.
> 
> Andre

Okay I think I have figured it out, but I am not sure what a good
solution is.

I think the problem is the fact that the keys may not be initialized
until init_default_flow_dissectors is called and I am not sure that is
happening before the network interface is trying to do DHCP.

I have to look at the initialization framework to verify if that is the
case.  It would make sense why I don't usually see it though since I
usually run igb as a module and that doesn't get loaded until later if
I am not mistaken.

- Alex