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

Vladimir Oltean
2021-03-20T11:20:30Z

On Fri, Mar 19, 2021 at 03:20:38PM -0700, Florian Fainelli wrote:
>
>
> 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 ;)

Well, it comes preinstalled on my system, I don't need it, and it has
caused me nothing but trouble. So I think it has earned its title :D

> > 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?

Sure, I'll change the return values of the shims everywhere.

> > +}
> > #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?

The trouble is that br_mdb_switchdev_host calls switchdev_port_obj_add,
and I think the agreement was that replayed events should be a silent,
one-to-one conversation via a direct call to the notifier block of the
interested driver, as opposed to a call to the entire notifier chain
which would make everybody else in the system see duplicates. This is
the reason why I duplicated mostly everything.