Re: [PATCH net-next-2.6] bridge: add __rcu annotations

[Stephen Hemminger <shemminger@linux-foundation.org>]

On Sat, 13 Nov 2010 18:58:50 +0100
Eric Dumazet <eric.dumazet@gmail.com> wrote:

> Le samedi 13 novembre 2010 à 09:35 -0800, Stephen Hemminger a écrit :
> > On Sat, 13 Nov 2010 09:15:28 +0100
> > Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > 
> > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > > index 578debb..ffbd177 100644
> > > --- a/include/linux/netdevice.h
> > > +++ b/include/linux/netdevice.h
> > > @@ -996,7 +996,10 @@ struct net_device {
> > >  #endif
> > >  
> > >  	rx_handler_func_t	*rx_handler;
> > > -	void			*rx_handler_data;
> > > +	union {
> > > +		void				*rx_handler_data;
> > > +		struct net_bridge_port __rcu	*br_port_rcu;
> > > +	};
> > >  
> > >  	struct netdev_queue __rcu *ingress_queue;
> > 
> > I don't like making the generic hook typed again.
> > We don't do this for other callbacks, timers, workqueues, ...
> > Why is it necessary for RCU notation.
> > 
> 
> because rcu_dereference() needs the type for __CHECKER__/sparse checks
> 
> #define __rcu_dereference_check(p, c, space) \
>         ({ \
>                 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
>                 rcu_lockdep_assert(c); \
>                 rcu_dereference_sparse(p, space); \
>                 smp_read_barrier_depends(); \
>                 ((typeof(*p) __force __kernel *)(_________p1)); \
>         })
> 
> So using a "void *ptr" is not an option
> 
> Its also cleaner to use
> 
> rcu_dereference(dev->br_port_rcu)
> 
> instead of 
> 
> (struct net_bridge_port *)rcu_dereference(dev->rx_handler_data)

There must be a better way. What about use of that hook by macvlan and openvswitch?



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