linux-kernel - Re: [PATCH V3 net-next 3/4] net: dsa: mv88e6xxx: mac-auth/MAB implementation

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Date:   Wed, 6 Jul 2022 16:28:34 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Hans S <schultz.hans@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Hans Schultz <schultz.hans+netdev@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Shuah Khan <shuah@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Ido Schimmel <idosch@...dia.com>, linux-kernel@...r.kernel.org,
        bridge@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH V3 net-next 3/4] net: dsa: mv88e6xxx: mac-auth/MAB
 implementation

On Tue, Jul 05, 2022 at 05:05:52PM +0200, Hans S wrote:
> Hi, does anybody know what it going on with this variable?
> struct dsa_port *dp ->ageing_time;
> 
> I experience that it changes value like a factor ~10 at times.

Could you be a bit more specific? Are you talking about STP Topology
Change Notification BPDUs, which trigger this code path?

diff --git a/net/bridge/br_stp.c b/net/bridge/br_stp.c
index 7d27b2e6038f..9b25bc2dcb3e 100644
--- a/net/bridge/br_stp.c
+++ b/net/bridge/br_stp.c
@@ -671,10 +671,10 @@ void __br_set_topology_change(struct net_bridge *br, unsigned char val)
 
 		if (val) {
 			t = 2 * br->forward_delay;
-			br_debug(br, "decreasing ageing time to %lu\n", t);
+			br_info(br, "decreasing ageing time to %lu\n", t);
 		} else {
 			t = br->bridge_ageing_time;
-			br_debug(br, "restoring ageing time to %lu\n", t);
+			br_info(br, "restoring ageing time to %lu\n", t);
 		}
 
 		err = __set_ageing_time(br->dev, t);

Coincidentally the default values of 2 * br->forward_delay and br->bridge_ageing_time
are 1 order of magnitude apart from each other.

[  139.998310] br0: topology change detected, propagating
[  140.003490] br0: decreasing ageing time to 3000
[  175.193054] br0: restoring ageing time to 30000

What's the problem anyway?