• Curt Brune's avatar
    bridge: use spin_lock_bh() in br_multicast_set_hash_max · fe0d692b
    Curt Brune authored
    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>
    fe0d692b
br_multicast.c 44.4 KB