Re: [RFC PATCH v2 net-next 09/16] net: dsa: replay port and local fdb entries when joining the bridge

On Mon, Mar 22, 2021 at 06:07:51PM +0100, Tobias Waldekranz wrote:

On Mon, Mar 22, 2021 at 18:19, Vladimir Oltean [off-list ref] wrote:

quoted

On Mon, Mar 22, 2021 at 04:44:41PM +0100, Tobias Waldekranz wrote:

quoted

I do not know if it is a problem or not, more of an observation: This is
not guaranteed to be an exact replay of the events that the bridge port
(i.e. bond0 or whatever) has received since, in fdb_insert, we exit
early when adding local entries if that address is already in the
database.

Do we have to guard against this somehow? Or maybe we should consider
the current behavior a bug and make sure to always send the event in the
first place?

I don't really understand what you're saying.
fdb_insert has:

	fdb = br_fdb_find(br, addr, vid);
	if (fdb) {
		/* it is okay to have multiple ports with same
		 * address, just use the first one.
		 */
		if (test_bit(BR_FDB_LOCAL, &fdb->flags))
			return 0;
		br_warn(br, "adding interface %s with same address as a received packet (addr:%pM, vlan:%u)\n",
		       source ? source->dev->name : br->dev->name, addr, vid);
		fdb_delete(br, fdb, true);
	}

	fdb = fdb_create(br, source, addr, vid,
			 BIT(BR_FDB_LOCAL) | BIT(BR_FDB_STATIC));

Basically, if the {addr, vid} pair already exists in the fdb, and it
points to a local entry, fdb_create is bypassed.

Whereas my br_fdb_replay() function iterates over br->fdb_list, which is
exactly where fdb_create() also lays its eggs. That is to say, unless
I'm missing something, that duplicate local FDB entries that skipped the
fdb_create() call in fdb_insert() because they were for already-existing
local FDB entries will also be skipped by br_fdb_replay(), because it
iterates over a br->fdb_list which contains unique local addresses.
Where am I wrong?

No you are right. I was thinking back to my attempt of offloading local
addresses and I distinctly remembered that local addresses could be
added without a notification being sent.

But that is not what is happening. It is just already inserted on
another port. So the notification would reach DSA, or not, depending on
ordering the of events. But there will be no discrepancy between that
and the replay.

I'm not saying that the bridge isn't broken, because it is, but for
different reasons, as explained here:
https://patchwork.kernel.org/project/netdevbpf/patch/20210224114350.2791260-9-olteanv@gmail.com/

What I can do is I can make br_switchdev_fdb_notify() skip fdb entries
with the BR_FDB_LOCAL bit set, and target that patch against "net", with
a Fixes: tag of 6b26b51b1d13 ("net: bridge: Add support for notifying
devices about FDB add/del").
Then I can also skip the entries with BR_FDB_LOCAL from br_fdb_replay.
Then, when I return to the "RX filtering for DSA" series, I can add the
"is_local" bit to switchdev FDB objects, and make all drivers reject
"is_local" entries (which is what the linked patch does) unless more
specific treatment is applied to those (trap to CPU).
Nikolay?