From mboxrd@z Thu Jan  1 00:00:00 1970
From: "David S. Miller" <davem@redhat.com>
Subject: Re: 2.6.7-rc3: unregister_netdevice: waiting for tun0 to become
 free. Usage count = 1
Date: Thu, 17 Jun 2004 10:10:16 -0700
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To: Herbert Xu <herbert@gondor.apana.org.au>
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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.