[PATCH 091/115] bridge: fix race with topology change timer

[Luis Henriques]

3.5.7.13 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: stephen hemminger <stephen at networkplumber.org>

commit 83401eb4990ff6af55aeed8f49681558544192e6 upstream.

A bridge should only send topology change notice if it is not
the root bridge. It is possible for message age timer to elect itself
as a new root bridge, and still have a topology change timer running
but waiting for bridge lock on other CPU.

Solve the race by checking if we are root bridge before continuing.
This was the root cause of the cases where br_send_tcn_bpdu would OOPS.

Reported-by: JerryKang <jerry.kang at samsung.com>
Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/bridge/br_stp_timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bridge/br_stp_timer.c b/net/bridge/br_stp_timer.c
index a6747e6..acc63a4 100644
--- a/net/bridge/br_stp_timer.c
+++ b/net/bridge/br_stp_timer.c
@@ -107,7 +107,7 @@ static void br_tcn_timer_expired(unsigned long arg)
 
 	br_debug(br, "tcn timer expired\n");
 	spin_lock(&br->lock);
-	if (br->dev->flags & IFF_UP) {
+	if (!br_is_root_bridge(br) && (br->dev->flags & IFF_UP)) {
 		br_transmit_tcn(br);
 
 		mod_timer(&br->tcn_timer,jiffies + br->bridge_hello_time);
-- 
1.8.1.2