linux-kernel - Re: [PATCH tip/core/urgent 1/4] rcu: add rcu_access_pointer and rcu_dereference

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Message-ID: <20100409165735.GB2421@linux.vnet.ibm.com>
Date:	Fri, 9 Apr 2010 09:57:35 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Howells <dhowells@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu
Subject: Re: [PATCH tip/core/urgent 1/4] rcu: add rcu_access_pointer and
 rcu_dereference_protected

On Fri, Apr 09, 2010 at 11:24:18AM +0200, Eric Dumazet wrote:
> Le vendredi 09 avril 2010 à 10:10 +0100, David Howells a écrit :
> > Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> > 
> > > +#define rcu_access_pointer(p) ((void *)ACCESS_ONCE(p))
> > > ...
> > > +#define rcu_access_pointer(p)		((void *)ACCESS_ONCE(p))
> > 
> > There's no difference between your two versions of rcu_access_pointer(), so
> > you could move that whole construct outside of the #ifdef'ed section.
> > 
> > Other than that:
> > 
> > Acked-by: David Howells <dhowells@...hat.com>
> 
> I also prefer to keep type checking if possible
> 
> #define rcu_access_pointer(p)		(ACCESS_ONCE(p))

Yikes!  I was obsessing on preventing people from dereferencing the
pointer, but you are quite right, they might be comparing it to a
constant pointer to check for array bounds or for use of a statically
allocated emergency-pool item.

I will fix and resubmit.

> Other than that:
> 
> Acked-by: Eric Dumazet <eric.dumazet@...il.com>

							Thanx, Paul
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