bridge: send proper message_age in config BPDU

A bridge topology with three systems:

      +------+  +------+
      | A(2) |--| B(1) |
      +------+  +------+
           \    /
          +------+
          | C(3) |
          +------+

What is supposed to happen:
 * bridge with the lowest ID is elected root (for example: B)
 * C detects that A->C is higher cost path and puts in blocking state

What happens. Bridge with lowest id (B) is elected correctly as
root and things start out fine initially. But then config BPDU
doesn't get transmitted from A -> C. Because of that
the link from A-C is transistioned to the forwarding state.

The root cause of this is that the configuration messages
is generated with bogus message age, and dropped before
sending.

In the standardmessage_age is supposed to be:
  the time since the generation of the Configuration BPDU by
  the Root that instigated the generation of this Configuration BPDU.

Reimplement this by recording the timestamp (age + jiffies) when
recording config information. The old code incorrectly used the time
elapsed on the ageing timer which was incorrect.

See also:
  https://bugzilla.vyatta.com/show_bug.cgi?id=7164

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/net/bridge/br_stp.c b/net/bridge/br_stp.c
index bb4383e84de9..fcff62251547 100644
--- a/net/bridge/br_stp.c
+++ b/net/bridge/br_stp.c
@@ -164,8 +164,7 @@ void br_transmit_config(struct net_bridge_port *p)
         else {
                 struct net_bridge_port *root
                         = br_get_port(br, br->root_port);
-                bpdu.message_age = br->max_age
-                        - (root->message_age_timer.expires - jiffies)
+                bpdu.message_age = (jiffies - root->designated_age)
                         + MESSAGE_AGE_INCR;
         }
         bpdu.max_age = br->max_age;
@@ -189,6 +188,7 @@ static inline void br_record_config_information(struct net_bridge_port *p,
         p->designated_cost = bpdu->root_path_cost;
         p->designated_bridge = bpdu->bridge_id;
         p->designated_port = bpdu->port_id;
+        p->designated_age = jiffies + bpdu->message_age;
 
         mod_timer(&p->message_age_timer, jiffies
                   + (p->br->max_age - bpdu->message_age));