Commit fe0d692b authored by Curt Brune's avatar Curt Brune Committed by David S. Miller

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: default avatarCurt Brune <curt@cumulusnetworks.com>
Signed-off-by: default avatarScott Feldman <sfeldma@cumulusnetworks.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 88ad3149
...@@ -1998,7 +1998,7 @@ int br_multicast_set_hash_max(struct net_bridge *br, unsigned long val) ...@@ -1998,7 +1998,7 @@ int br_multicast_set_hash_max(struct net_bridge *br, unsigned long val)
u32 old; u32 old;
struct net_bridge_mdb_htable *mdb; struct net_bridge_mdb_htable *mdb;
spin_lock(&br->multicast_lock); spin_lock_bh(&br->multicast_lock);
if (!netif_running(br->dev)) if (!netif_running(br->dev))
goto unlock; goto unlock;
...@@ -2030,7 +2030,7 @@ int br_multicast_set_hash_max(struct net_bridge *br, unsigned long val) ...@@ -2030,7 +2030,7 @@ int br_multicast_set_hash_max(struct net_bridge *br, unsigned long val)
} }
unlock: unlock:
spin_unlock(&br->multicast_lock); spin_unlock_bh(&br->multicast_lock);
return err; return err;
} }
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