Re: [RFC] netdev sysfs failure handling

[Stephen Hemminger <shemminger@osdl.org>]

On Tue, 09 May 2006 15:43:22 -0700 (PDT)
"David S. Miller" <davem@davemloft.net> wrote:

> From: Stephen Hemminger <shemminger@osdl.org>
> Date: Tue, 9 May 2006 14:40:49 -0700
> 
> > Agreed, especially since rtnl is now a real mutex.  The case, that
> > I was worried about:
> > 	rtnl_lock()
> > 	spin_lock_irq(&mylock);
> > 	x = register_netdevice();
> > ...
> > 
> > Doesn't show up in any current code, even for the pseudo devices
> > and funny virtualized interfaces.
> 
> Right, therefore I think we should put something like your patch in
> there now.... perhaps.
> 
> The case where we really needed the todo list is unregister, so that
> we can safely wait for all references to the net device to go away.
> 
> I still wonder about those mentioned hotplug races wrt. linkwatch
> in the comment above netdev_run_todo().
> 
> Linkwatch is such a nuissance because it combines asynchronous link
> state change processing with keventd and RTNL locking.  It sleeps
> waiting for __LINK_STATE_SCHED to clear with the RTNL held (via
> dev_deactivate()).  But then again dev_close() code paths do this
> too, so the dev_deactivate() bit should be OK.
> 
> Linkwatch, after doing the dev_activate(), emits a NETDEV_CHANGE
> notifier on netdev_chain and also sends out an RTM_NETLINK
> message.  This is for the case where IFF_UP is set.
> 
> Until we release the RTNL semaphore, during netdev register, nobody
> can go in an inspect the state of a net device.  So doing the sysfs
> node creation in register_netdevice() should be OK as far as I can
> tell.
> 
> Can anyone find a problem with this?

Also, by getting the netdevice fully in sysfs under RTNL,
we are safe from races with the hotplug uevent that occurs.

Right now, it might be possible on SMP for the hotplug to happen
after register_netdevice, but before the device shows up
in sysfs.