Re: [RFC PATCH v2 net-next 08/16] net: dsa: replay port and host-joined mdb entries when joining the bridge

Florian Fainelli
2021-03-19T22:21:23Z

On 3/18/2021 4:18 PM, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
>
> I have udhcpcd in my system and this is configured to bring interfaces
> up as soon as they are created.
>
> I create a bridge as follows:
>
> ip link add br0 type bridge
>
> As soon as I create the bridge and udhcpcd brings it up, I have some
> other crap (avahi)

How dare you ;)

that starts sending some random IPv6 packets to
> advertise some local services, and from there, the br0 bridge joins the
> following IPv6 groups:
>
> 33:33:ff:6d:c1:9c vid 0
> 33:33:00:00:00:6a vid 0
> 33:33:00:00:00:fb vid 0
>
> br_dev_xmit
> -> br_multicast_rcv
> -> br_ip6_multicast_add_group
> -> __br_multicast_add_group
> -> br_multicast_host_join
> -> br_mdb_notify
>
> This is all fine, but inside br_mdb_notify we have br_mdb_switchdev_host
> hooked up, and switchdev will attempt to offload the host joined groups
> to an empty list of ports. Of course nobody offloads them.
>
> Then when we add a port to br0:
>
> ip link set swp0 master br0
>
> the bridge doesn't replay the host-joined MDB entries from br_add_if,
> and eventually the host joined addresses expire, and a switchdev
> notification for deleting it is emitted, but surprise, the original
> addition was already completely missed.
>
> The strategy to address this problem is to replay the MDB entries (both
> the port ones and the host joined ones) when the new port joins the
> bridge, similar to what vxlan_fdb_replay does (in that case, its FDB can
> be populated and only then attached to a bridge that you offload).
> However there are 2 possibilities: the addresses can be 'pushed' by the
> bridge into the port, or the port can 'pull' them from the bridge.
>
> Considering that in the general case, the new port can be really late to
> the party, and there may have been many other switchdev ports that
> already received the initial notification, we would like to avoid
> delivering duplicate events to them, since they might misbehave. And
> currently, the bridge calls the entire switchdev notifier chain, whereas
> for replaying it should just call the notifier block of the new guy.
> But the bridge doesn't know what is the new guy's notifier block, it
> just knows where the switchdev notifier chain is. So for simplification,
> we make this a driver-initiated pull for now, and the notifier block is
> passed as an argument.
>
> To emulate the calling context for mdb objects (deferred and put on the
> blocking notifier chain), we must iterate under RCU protection through
> the bridge's mdb entries, queue them, and only call them once we're out
> of the RCU read-side critical section.
>
> Suggested-by: Ido Schimmel <idosch@idosch.org>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> ---
> include/linux/if_bridge.h | 9 +++++
> net/bridge/br_mdb.c | 84 +++++++++++++++++++++++++++++++++++++++
> net/dsa/dsa_priv.h | 2 +
> net/dsa/port.c | 6 +++
> net/dsa/slave.c | 2 +-
> 5 files changed, 102 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/if_bridge.h b/include/linux/if_bridge.h
> index ebd16495459c..4c25dafb013d 100644
> --- a/include/linux/if_bridge.h
> +++ b/include/linux/if_bridge.h
> @@ -69,6 +69,8 @@ bool br_multicast_has_querier_anywhere(struct net_device *dev, int proto);
> bool br_multicast_has_querier_adjacent(struct net_device *dev, int proto);
> bool br_multicast_enabled(const struct net_device *dev);
> bool br_multicast_router(const struct net_device *dev);
> +int br_mdb_replay(struct net_device *br_dev, struct net_device *dev,
> + struct notifier_block *nb, struct netlink_ext_ack *extack);
> #else
> static inline int br_multicast_list_adjacent(struct net_device *dev,
> struct list_head *br_ip_list)
> @@ -93,6 +95,13 @@ static inline bool br_multicast_router(const struct net_device *dev)
> {
> return false;
> }
> +static inline int br_mdb_replay(struct net_device *br_dev,
> + struct net_device *dev,
> + struct notifier_block *nb,
> + struct netlink_ext_ack *extack)
> +{
> + return -EINVAL;

Should we return -EOPNOTUSPP such that this is not made fatal for DSA if
someone compiles its kernel with CONFIG_BRIDGE_IGMP_SNOOPING disabled?

> +}
> #endif
>
> #if IS_ENABLED(CONFIG_BRIDGE) && IS_ENABLED(CONFIG_BRIDGE_VLAN_FILTERING)
> diff --git a/net/bridge/br_mdb.c b/net/bridge/br_mdb.c
> index 8846c5bcd075..23973186094c 100644
> --- a/net/bridge/br_mdb.c
> +++ b/net/bridge/br_mdb.c
> @@ -506,6 +506,90 @@ static void br_mdb_complete(struct net_device *dev, int err, void *priv)
> kfree(priv);
> }
>
> +static int br_mdb_replay_one(struct notifier_block *nb, struct net_device *dev,
> + struct net_bridge_mdb_entry *mp, int obj_id,
> + struct net_device *orig_dev,
> + struct netlink_ext_ack *extack)
> +{
> + struct switchdev_notifier_port_obj_info obj_info = {
> + .info = {
> + .dev = dev,
> + .extack = extack,
> + },
> + };
> + struct switchdev_obj_port_mdb mdb = {
> + .obj = {
> + .orig_dev = orig_dev,
> + .id = obj_id,
> + },
> + .vid = mp->addr.vid,
> + };
> + int err;
> +
> + if (mp->addr.proto == htons(ETH_P_IP))
> + ip_eth_mc_map(mp->addr.dst.ip4, mdb.addr);
> +#if IS_ENABLED(CONFIG_IPV6)
> + else if (mp->addr.proto == htons(ETH_P_IPV6))
> + ipv6_eth_mc_map(&mp->addr.dst.ip6, mdb.addr);
> +#endif
> + else
> + ether_addr_copy(mdb.addr, mp->addr.dst.mac_addr);

How you would feel about re-using br_mdb_switchdev_host_port() here and
pass a 'type' value that is neither RTM_NEWDB nor RTM_DELDB just so you
don't have to duplicate that code here and we ensure it is in sync?
--
Florian