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

[Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>]

Hello!

> > bug. It makes sense to think about waiting for at least one quiescent
> > state after detaching the stale device from dst and real dev_put() it.
> > Reference to RCU is not occasional, the job looks natural for it.
> 
> It seems a simple synchronize_kernel() would clear all the
> crap no?

Sort of. I think it should happen after killing reference to dst->dev:

+                       dst->dev = &loopback_dev;
+                       dev_hold(&loopback_dev);


but before dropping reference to dev:

+                       dev_put(dev);


So, I think it should look like:

                dst->dev = &loopback_dev;
                dev_hold(&loopback_dev);
+               synchronize_kernel();
                dev_put(dev);

(sorry, I still do not have Herbert's patch pulled)

Alexey