netdev - Re: [PATCH net-next-2.6] bridge: add _

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Date:	Sat, 13 Nov 2010 18:58:50 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next-2.6] bridge: add __rcu annotations

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@...il.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)



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