Subject: Re: [PATCH net] bridge: notify user space of fdb port change

From: Stephen Hemminger <[email-masked]>
Date: Tue, 13 May 2014 08:28:53 -0700

On Tue, 13 May 2014 17:16:11 +0200
Jiri Pirko <[email-masked]> wrote:

> Tue, May 13, 2014 at 09:55:08AM CEST, [email-masked] wrote:
> >From: Jon Maxwell <[email-masked]>
> >
> >There has been a number incidents recently where customers running KVM have 
> >reported that VM hosts on different Hypervisors are unreachable. Based on 
> >pcap traces we found that the bridge was broadcasting the ARP request out 
> >onto the network. However some NICs have an inbuilt switch which on occasions 
> >were broadcasting the VMs ARP request back through the physical NIC on the 
> >Hypervisor. This resulted in the bridge changing ports and incorrectly learning
> >that the VMs mac address was external. As a result the ARP reply was directed 
> >back onto the external network and VM never updated it's ARP cache. This patch 
> >will notify the bridge command to identify such port toggling.
> >
> >Signed-off-by: Jon Maxwell <[email-masked]>
> >---
> > net/bridge/br_fdb.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> >diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
> >index 9203d5a..37742e2 100644
> >--- a/net/bridge/br_fdb.c
> >+++ b/net/bridge/br_fdb.c
> >@@ -507,6 +507,8 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
> > 					source->dev->name);
> > 		} else {
> > 			/* fastpath: update of existing entry */
> >+			if (source->port_no != fdb->dst->port_no)
> >+				fdb_notify(br, fdb, RTM_NEWNEIGH);
> > 			fdb->dst = source;
> > 			fdb->updated = jiffies;
> > 			if (unlikely(added_by_user))
> >-- 
> >1.8.3.1
> 
> 
> Reviewed-by: Jiri Pirko <[email-masked]>

I like the patch, but please add unlikely() to this conditional.
This is in the fast path code for bridge learning.