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bridge: use spin_lock_bh() in br_multicast_set_hash_max

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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>
This commit is contained in:
Curt Brune 2014-01-06 11:00:32 -08:00 committed by David S. Miller
parent 88ad31491e
commit fe0d692bbc
1 changed files with 2 additions and 2 deletions
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4
net/bridge/br_multicast.c
View file

@ -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 @@ int br_multicast_set_hash_max(struct net_bridge *br, unsigned long val)
}
unlock:
spin_unlock(&br->multicast_lock);
spin_unlock_bh(&br->multicast_lock);
return err;
}