Re: [RFC PATCH v2 net-next 01/17] net: dsa: reference count the host mdb addresses

[Tobias Waldekranz <tobias@waldekranz.com>]

On Wed, Feb 24, 2021 at 13:43, Vladimir Oltean <olteanv@gmail.com> wrote:
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
>
> Currently any DSA switch that is strict when implementing the mdb
> operations prints these benign errors after the addresses expire, with
> at least 2 ports bridged:
>
> [  286.013814] mscc_felix 0000:00:00.5 swp3: failed (err=-2) to del object (id=3)
>
> The reason has to do with this piece of code:
>
> 	netdev_for_each_lower_dev(dev, lower_dev, iter)
> 		br_mdb_switchdev_host_port(dev, lower_dev, mp, type);
>
> called from:
>
> br_multicast_group_expired
> -> br_multicast_host_leave
>    -> br_mdb_notify
>       -> br_mdb_switchdev_host
>
> Basically, the bridge code is correct.

How about "the bridge code is not wrong"? Is there any reason why we
could not get rid of the duplicated messages at the source
(br_mdb_switchdev_host)?

The forward offloading we have talked about before requires that the
bridge-internal port OFMs are bounded to some low value
(e.g. BITS_PER_LONG) such that they can be tracked in a small
bitfield. I have a patch that does this, it is tiny.

With that in place, imagine a `br_switchdev_for_each_distinct_dev`
helper that would wrap `netdev_for_each_lower_dev`, keeping track of
OFMs it had already visited.

For all host related switchdev calls, we should be able to use that
instead of the full iterator to only contact each switchdev driver once.