Linux Ethernet Bridging - Sep 2020 - [Bridge] [PATCH net] net: bridge: fdb: don't flush ext_learn entries

From: Nikolay Aleksandrov <nikolay at nvidia.com>

When a user-space software manages fdb entries externally it should
set the ext_learn flag which marks the fdb entry as externally managed
and avoids expiring it (they're treated as static fdbs). Unfortunately
on events where fdb entries are flushed (STP down, netlink fdb flush
etc) these fdbs are also deleted automatically by the bridge. That in turn
causes trouble for the managing user-space software (e.g. in MLAG setups
we lose remote fdb entries on port flaps).
These entries are completely externally managed so we should avoid
automatically deleting them, the only exception are offloaded entries
(i.e. BR_FDB_ADDED_BY_EXT_LEARN + BR_FDB_OFFLOADED). They are flushed as
before.

Fixes: eb100e0e24a2 ("net: bridge: allow to add externally learned entries
from user-space")
Signed-off-by: Nikolay Aleksandrov <nikolay at nvidia.com>
---
 net/bridge/br_fdb.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index 9db504baa094..32ac8343b0ba 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -413,6 +413,8 @@ void br_fdb_delete_by_port(struct net_bridge *br,
 
 		if (!do_all)
 			if (test_bit(BR_FDB_STATIC, &f->flags) ||
+			    (test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &f->flags) &&
+			     !test_bit(BR_FDB_OFFLOADED, &f->flags)) ||
 			    (vid && f->key.vlan_id != vid))
 				continue;
 
-- 
2.26.2

From: Nikolay Aleksandrov <razor at blackwall.org>
Date: Mon, 28 Sep 2020 18:30:02 +0300
> From: Nikolay Aleksandrov <nikolay at nvidia.com>
> 
> When a user-space software manages fdb entries externally it should
> set the ext_learn flag which marks the fdb entry as externally managed
> and avoids expiring it (they're treated as static fdbs). Unfortunately
> on events where fdb entries are flushed (STP down, netlink fdb flush
> etc) these fdbs are also deleted automatically by the bridge. That in turn
> causes trouble for the managing user-space software (e.g. in MLAG setups
> we lose remote fdb entries on port flaps).
> These entries are completely externally managed so we should avoid
> automatically deleting them, the only exception are offloaded entries
> (i.e. BR_FDB_ADDED_BY_EXT_LEARN + BR_FDB_OFFLOADED). They are flushed as
> before.
> 
> Fixes: eb100e0e24a2 ("net: bridge: allow to add externally learned
entries from user-space")
> Signed-off-by: Nikolay Aleksandrov <nikolay at nvidia.com>
Applied and queued up for -stable, thank you.