[PATCH net] net: bridge: start hello timer only if device is up

[Nikolay Aleksandrov <nikolay@cumulusnetworks.com>]

When the transition of NO_STP -> KERNEL_STP was fixed by always calling
mod_timer in br_stp_start, it introduced a new regression which causes
the timer to be armed even when the bridge is down, and since we stop
the timers in its ndo_stop() function, they never get disabled if the
device is destroyed before it's upped.

To reproduce:
$ while :; do ip l add br0 type bridge hello_time 100; brctl stp br0 on;
ip l del br0; done;

CC: Xin Long <lucien.xin@gmail.com>
CC: Ivan Vecera <cera@cera.cz>
CC: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reported-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Fixes: 6d18c732b95c ("bridge: start hello_timer when enabling KERNEL_STP in br_stp_start")
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
---
Sebastian it'd be great if you can test the patch as well.

 net/bridge/br_stp_if.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
index 4efd5d54498a..89110319ef0f 100644
--- a/net/bridge/br_stp_if.c
+++ b/net/bridge/br_stp_if.c
@@ -173,7 +173,8 @@ static void br_stp_start(struct net_bridge *br)
 		br_debug(br, "using kernel STP\n");
 
 		/* To start timers on any ports left in blocking */
-		mod_timer(&br->hello_timer, jiffies + br->hello_time);
+		if (br->dev->flags & IFF_UP)
+			mod_timer(&br->hello_timer, jiffies + br->hello_time);
 		br_port_state_selection(br);
 	}
 
-- 
2.1.4