linux-kernel - Re: [PATCH net] bridge: notify user space after fdb update

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Message-ID: <5385FA83.3080301@redhat.com>
Date:	Wed, 28 May 2014 11:02:27 -0400
From:	Vlad Yasevich <vyasevic@...hat.com>
To:	Jon Maxwell <jmaxwell37@...il.com>, stephen@...workplumber.org
CC:	davem@...emloft.net, makita.toshiaki@....ntt.co.jp,
	bridge@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, jpirko@...hat.com,
	jmaxwell@...hat.com
Subject: Re: [PATCH net] bridge: notify user space after fdb update

On 05/27/2014 06:45 PM, Jon Maxwell wrote:
> 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, after a fdb has been updated to identify such
> port toggling.
> 
> Signed-off-by: Jon Maxwell <jmaxwell37@...il.com>
> ---
>  net/bridge/br_fdb.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
> index 9203d5a..f3ee2da 100644
> --- a/net/bridge/br_fdb.c
> +++ b/net/bridge/br_fdb.c
> @@ -487,6 +487,7 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
>  {
>  	struct hlist_head *head = &br->hash[br_mac_hash(addr, vid)];
>  	struct net_bridge_fdb_entry *fdb;
> +	bool fdb_modified = 0;
>  
>  	/* some users want to always flood. */
>  	if (hold_time(br) == 0)
> @@ -507,10 +508,15 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
>  					source->dev->name);
>  		} else {
>  			/* fastpath: update of existing entry */
> -			fdb->dst = source;
> +			if (unlikely(source != fdb->dst)) {
> +					fdb->dst = source;
> +					fdb_modified = 1;
> +				}

This looks over-indented.

-vlad

>  			fdb->updated = jiffies;
>  			if (unlikely(added_by_user))
>  				fdb->added_by_user = 1;
> +			if (unlikely(fdb_modified))
> +				fdb_notify(br, fdb, RTM_NEWNEIGH);
>  		}
>  	} else {
>  		spin_lock(&br->hash_lock);
> 

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