Date:	Tue, 8 Mar 2011 08:42:47 -0500
From:	Andy Gospodarek <andy@...yhouse.net>
To:	Jiri Pirko <jpirko@...hat.com>
Cc:	Andy Gospodarek <andy@...yhouse.net>,
	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>, netdev@...r.kernel.org,
	davem@...emloft.net, shemminger@...ux-foundation.org,
	kaber@...sh.net, fubar@...ibm.com, eric.dumazet@...il.com
Subject: Re: [patch net-next-2.6] net: reinject arps into bonding slave
	instead of master

On Tue, Mar 08, 2011 at 08:13:51AM +0100, Jiri Pirko wrote:
> Mon, Mar 07, 2011 at 11:43:38PM CET, andy@...yhouse.net wrote:
[...]
> >
> >This patch doesn't work.
> >
> >My setup has bond0.100 -> bond0 -> eth2 and eth3.  ARP monitoring is
> >enabled as is arp_valiate.
> >
> >The initial problem was just that just before vlan_on_bond_hook is
> >called, skb->dev = bond0.100 and orig_dev = eth2.   (This is after
> >running goto another_route and having been called back through
> >__netif_receive_skb since vlan_hwaccel_do_receive it true.)
> >
> >Now vlan_on_bond_hook is called and we have 2 skbs.
> >
> >The original skb still have skb->dev = bond0.100 and orig_dev = eth2.
> >Since bond_arp_rcv is registered for traffic only to bond0, the handler
> >is not hit and the frame is dropped (or processed by another handler).
> >
> >The cloned skb has skb->dev = bond0 and is put back on the receive queue
> >and comes back through __netif_receive_skb.  This frame will match the
> >ptype entry for bond_arp_rcv, but since orig_dev = bond0 in this case,
> >the code in bond_arp_rcv will not handle the frame.  
> >
> >If we truly want to track the original interface that received the
> >frame, the following is a better option.  With the recursive nature of
> >__netif_receive_skb at this point, we should really consider setting
> >orig_dev from skb_iif rather than just from skb->dev.
> >
> >diff --git a/net/core/dev.c b/net/core/dev.c
> >index 30440e7..500fdbc 100644
> >--- a/net/core/dev.c
> >+++ b/net/core/dev.c
> >@@ -3135,7 +3135,6 @@ static int __netif_receive_skb(struct sk_buff *skb)
> > 
> > 	if (!skb->skb_iif)
> > 		skb->skb_iif = skb->dev->ifindex;
> >-	orig_dev = skb->dev;
> > 
> > 	skb_reset_network_header(skb);
> > 	skb_reset_transport_header(skb);
> >@@ -3145,6 +3144,7 @@ static int __netif_receive_skb(struct sk_buff *skb)
> > 
> > 	rcu_read_lock();
> > 
> >+	orig_dev = dev_get_by_index_rcu(dev_net(skb->dev),skb->skb_iif);
> > another_round:
> > 
> > 	__this_cpu_inc(softnet_data.processed);
> >
> 
> This was proposed earlier. people did not like this very much :(
> 

Interesting.  I'll have to look back at the discussion.

> I forgot to include crucial part of "goto another_round for vlan".
> Following patch should work (will test it once I get to work):
> 
> Subject: [patch net-next 2.6] net: reinject arps into bonding slave instead of master
> 
> Recent patch "bonding: move processing of recv handlers into
> handle_frame()" caused a regression on following net scheme:
> 
> eth0 - bond0 - bond0.5
> 
> where arp monitoring is happening over vlan. This patch fixes it by
> reinjecting the arp packet into bonding slave device so the bonding
> rx_handler can pickup and process it.
> 
> also instead of calling __netif_receive_skb recursively, "goto another
> round" does this recursion. The point is the orig_dev variable remains
> intact.
> 
> Signed-off-by: Jiri Pirko <jpirko@...hat.com>
> ---
>  net/core/dev.c |   11 +++++------
>  1 files changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index c71bd18..ec330e1 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3094,12 +3094,12 @@ void netdev_rx_handler_unregister(struct net_device *dev)
>  }
>  EXPORT_SYMBOL_GPL(netdev_rx_handler_unregister);
>  
> -static void vlan_on_bond_hook(struct sk_buff *skb)
> +static void vlan_on_bond_hook(struct sk_buff *skb, struct net_device *orig_dev)
>  {
>  	/*
>  	 * Make sure ARP frames received on VLAN interfaces stacked on
>  	 * bonding interfaces still make their way to any base bonding
> -	 * device that may have registered for a specific ptype.
> +	 * device by reinjecting the frame into bonding slave (orig_dev)
>  	 */
>  	if (skb->dev->priv_flags & IFF_802_1Q_VLAN &&
>  	    vlan_dev_real_dev(skb->dev)->priv_flags & IFF_BONDING &&
> @@ -3108,7 +3108,7 @@ static void vlan_on_bond_hook(struct sk_buff *skb)
>  
>  		if (!skb2)
>  			return;
> -		skb2->dev = vlan_dev_real_dev(skb->dev);
> +		skb2->dev = orig_dev;
>  		netif_rx(skb2);
>  	}
> 

I'm pretty sure this patch will have the same catastrophic problem your
last one did.  By cloning and setting skb2->dev = orig_dev you just
inserted a frame identical to the one we received right back into the
stack.  It only took a few minutes for my box to melt as one frame on
the wire will cause an infinite number of frames to be received by the
stack.

> @@ -3196,13 +3196,12 @@ ncls:
>  			pt_prev = NULL;
>  		}
>  		if (vlan_hwaccel_do_receive(&skb)) {
> -			ret = __netif_receive_skb(skb);
> -			goto out;
> +			goto another_round;
>  		} else if (unlikely(!skb))
>  			goto out;
>  	}
>  
> -	vlan_on_bond_hook(skb);
> +	vlan_on_bond_hook(skb, orig_dev);
>  
>  	/* deliver only exact match when indicated */
>  	null_or_dev = deliver_exact ? skb->dev : NULL;
--
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