From: "John Kacur" <redacted>
Date: Mon, 11 Aug 2008 15:11:46 +0200

__qdisc_run() calls qdisc_restart() which calls
handle_dev_cpu_collision(skb, dev, q); and then the problem shows up
here:
__get_cpu_var(netdev_rx_stat).cpu_collision++;

The solution is to disable interrupts around the above increment. Here
is an attached patch to do so. (Thank's to Peter Zijlstra for help in
the analysis and dropping the answer in my lap, so if I got it right
it is due to his help, but if I messed it up, then I did that part all
by myself.)

__qdisc_run() always runs in software interrupt context,
so I guess this is some problem with the -rt stuff running
software interrupts in threads?