netdev - Re: [PATCH 0/5] bridge: RCU annotation and cleanup

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Date:	Mon, 15 Nov 2010 14:33:07 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	shemminger@...tta.com, davem@...emloft.net, netdev@...r.kernel.org,
	bridge@...ts.linux-foundation.org
Subject: Re: [PATCH 0/5] bridge: RCU annotation and cleanup

Le lundi 15 novembre 2010 à 21:23 +0900, Tetsuo Handa a écrit :
> Stephen Hemminger wrote:
> > This is a split up of what Eric did with a couple of small changes and additions.
> Something seems to be wrong with this patchset.
> 
> --- a/net/bridge/br_input.c
> +++ b/net/bridge/br_input.c
> > @@ -173,8 +177,8 @@ forward:
> >  	switch (p->state) {
> >  	case BR_STATE_FORWARDING:
> >  		rhook = rcu_dereference(br_should_route_hook);
> > -		if (rhook != NULL) {
> > -			if (rhook(skb))
> > +		if (rhook) {
> > +			if ((*rhook)(skb))
> 
> Is *rhook != NULL guaranteed when rhook != NULL?

Its the C standard convention, we call function pointed by rhook, not
*rhook.

$ cat func.c
typedef int (*hook_t)(int a1, int a2);

hook_t *hook;

int foo(int a1, int a2)
{
hook_t *handler = hook;

	if (handler)
		return handler(a1, a2);
	return 0;
}
$ gcc -O2 -c func.c
func.c: In function ‘foo’:
func.c:10:17: error: called object ‘handler’ is not a function


Now, if we use (*handler), it works :

$ cat func.c
typedef int (*hook_t)(int a1, int a2);

hook_t *hook;

int foo(int a1, int a2)
{
hook_t *handler = hook;

	if (handler)
		return (*handler)(a1, a2);
	return 0;
}
$ gcc -O2 -c func.c
$



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