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

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Message-ID: <20100408164615.GA4836@linux.vnet.ibm.com>
Date:	Thu, 8 Apr 2010 09:46:15 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	David Howells <dhowells@...hat.com>
Cc:	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,
	eric.dumazet@...il.com
Subject: Re: [PATCH tip/urgent] rcu: add rcu_access_pointer and
 rcu_dereference_protected

On Wed, Apr 07, 2010 at 04:00:09PM -0700, Paul E. McKenney wrote:
> On Wed, Apr 07, 2010 at 06:20:48PM +0100, David Howells wrote:
> > Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> > 
> > > In other cases, there will be a reference counter or a "not yet fully
> > > initialized" flag that can (and should) be tested.
> > 
> > Why would you be using rcu_access_pointer() there?  Why wouldn't you be using
> > rcu_dereference_protected()?
> 
> Excellent question.  I am writing up the documentation now, and will
> either (1) have a good use case or (2) remove the condition.

And all of the examples I could come up with that had c!=1 were contorted,
even by my standards.  So you were right, and I will drop the "c" on my
next set of patches.

							Thanx, Paul
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