From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Fri, 30 Nov 2007 00:04:20 +1100
From: Herbert Xu <herbert@gondor.apana.org.au>
Subject: Re: [PATCH (resubmit)][BRIDGE] Properly dereference the
	br_should_route_hook
Message-ID: <20071129130420.GA8487@gondor.apana.org.au>
References: <474C43F4.5080704@openvz.org>
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To: Pavel Emelyanov <xemul@openvz.org>
Cc: Linux Netdev List <netdev@vger.kernel.org>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, bridge@lists.osdl.org, devel@openvz.org

On Tue, Nov 27, 2007 at 07:21:08PM +0300, Pavel Emelyanov wrote:
> This hook is protected with the RCU, so simple
> 
> 	if (br_should_route_hook)
> 		br_should_route_hook(...)
> 
> is not enough on some architectures.
> 
> Use the rcu_dereference/rcu_assign_pointer in this case.
> 
> Fixed Stephen's comment concerning using the typeof().
> 
> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

Applied to net-2.6.  Thanks Pavel!

>  static void __exit ebtable_broute_fini(void)
>  {
> -	br_should_route_hook = NULL;
> +	rcu_assign_pointer(br_should_route_hook, NULL);

Just for the record, rcu_assign_pointer is never necessary when
you're assigning NULL.  The reason is that rcu_assign_pointer serves
as a barrier between the initialisation of the content of what you're
assigning and the actual assignment.  Since NULL does not need to be
initialised you don't need the barrier :)

Hmm, perhaps we could even build this logic into rcu_assign_pointer.

Then again, who still uses an Alpha? Mine died years ago :)

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
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