bridge: use spin_lock_bh() in br_multicast_set_hash_max

br_multicast_set_hash_max() is called from process context in
net/bridge/br_sysfs_br.c by the sysfs store_hash_max() function.

br_multicast_set_hash_max() calls spin_lock(&br->multicast_lock),
which can deadlock the CPU if a softirq that also tries to take the
same lock interrupts br_multicast_set_hash_max() while the lock is
held .  This can happen quite easily when any of the bridge multicast
timers expire, which try to take the same lock.

The fix here is to use spin_lock_bh(), preventing other softirqs from
executing on this CPU.

Steps to reproduce:

1. Create a bridge with several interfaces (I used 4).
2. Set the "multicast query interval" to a low number, like 2.
3. Enable the bridge as a multicast querier.
4. Repeatedly set the bridge hash_max parameter via sysfs.

  # brctl addbr br0
  # brctl addif br0 eth1 eth2 eth3 eth4
  # brctl setmcqi br0 2
  # brctl setmcquerier br0 1

  # while true ; do echo 4096 > /sys/class/net/br0/bridge/hash_max; done

Signed-off-by: Curt Brune <curt@cumulusnetworks.com>
Signed-off-by: Scott Feldman <sfeldma@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 4c214b2b88efa01d81be93a8b8d77e57229c1fa4..ef66365b7354da9f2fe2c4d87d2056d9a781f3c8 100644 (file)
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1998,7 +1998,7 @@ int br_multicast_set_hash_max(struct net_bridge *br, unsigned long val)
        u32 old;
        struct net_bridge_mdb_htable *mdb;
 
-       spin_lock(&br->multicast_lock);
+       spin_lock_bh(&br->multicast_lock);
        if (!netif_running(br->dev))
                goto unlock;
 
@@ -2030,7 +2030,7 @@ rollback:
        }
 
 unlock:
-       spin_unlock(&br->multicast_lock);
+       spin_unlock_bh(&br->multicast_lock);
 
        return err;
 }