The mac80211 module uses rcu_call() thus it should use rcu_barrier()
on module unload.

The rcu_barrier() is placed in mech.c ieee80211_stop_mesh() which is
invoked from ieee80211_stop() in case vif.type == NL80211_IFTYPE_MESH_POINT.
Acked-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NJesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>