From: Jarek Poplawski <redacted>
Date: Thu, 11 Jan 2007 08:24:28 +0100

Yesterday I did what I should do earlier - checked
this simple way, with printk, and now I have no doubts
it's a bug: if you add or remove vlan devices with
vconfig, register_vlan_device and unregister_vlan_dev
are called by ioctl and they use and change rcu
procetded data without preemption disabled so vlan
rcu hash lists could become corrupted or find results
could be wrong.

Those two operations do their modifications and changes under the RTNL
semaphore, via rtnl_lock() and rtnl_unlock() which guarentees that no
other modifications can occur.