[BRIDGE]: fix crash in STP

Bridge would crash because of uninitailized timer if STP is used and
device was inserted into a bridge before bridge was up. This got
introduced when the delayed port checking was added.  Fix is to not
enable STP on port unless bridge is up.

Bugzilla: http://bugzilla.kernel.org/show_bug.cgi?id=6140
Dup:      http://bugzilla.kernel.org/show_bug.cgi?id=6156

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

net/bridge/br_if.c

@@ -81,26 +81,27 @@ static void port_carrier_check(void *arg)
 {
 	struct net_device *dev = arg;
 	struct net_bridge_port *p;
+	struct net_bridge *br;
 
 	rtnl_lock();
 	p = dev->br_port;
 	if (!p)
 		goto done;
-
-	if (netif_carrier_ok(p->dev)) {
-		u32 cost = port_cost(p->dev);
-
-		spin_lock_bh(&p->br->lock);
-		if (p->state == BR_STATE_DISABLED) {
-			p->path_cost = cost;
-			br_stp_enable_port(p);
+	br = p->br;
+
+	if (netif_carrier_ok(dev))
+		p->path_cost = port_cost(dev);
+
+	if (br->dev->flags & IFF_UP) {
+		spin_lock_bh(&br->lock);
+		if (netif_carrier_ok(dev)) {
+			if (p->state == BR_STATE_DISABLED)
+				br_stp_enable_port(p);
+		} else {
+			if (p->state != BR_STATE_DISABLED)
+				br_stp_disable_port(p);
 		}
-		spin_unlock_bh(&p->br->lock);
-	} else {
-		spin_lock_bh(&p->br->lock);
-		if (p->state != BR_STATE_DISABLED)
-			br_stp_disable_port(p);
-		spin_unlock_bh(&p->br->lock);
+		spin_unlock_bh(&br->lock);
 	}
 done:
 	rtnl_unlock();