Re: 2.6.7-rc3: unregister_netdevice: waiting for tun0 to become free. Usage count = 1

["David S. Miller" <davem@xxxxxxxxxx>]

Herbert, you still don't understand what the synchronize_kernel() is
for.

It is to make sure that anyone (other cpus using the dst) who "saw"
the old dst->dev is done doing whatever they were doing _BEFORE_
we put the device reference.

The best we could do is accumulate devices to be put onto
some kind of list, then at the end of dst_ifdown() do one
synchronize_kernel() then walk the list putting all the
devices.