linux-kernel - Re: [PATCH 6/6] percpu-refcount: implement percpu_ref_reinit() and percpu_ref_is

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Message-ID: <20140619210733.GQ4904@linux.vnet.ibm.com>
Date:	Thu, 19 Jun 2014 14:07:33 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, cl@...ux-foundation.org,
	kmo@...erainc.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] percpu-refcount: implement percpu_ref_reinit() and
 percpu_ref_is_zero()

On Thu, Jun 19, 2014 at 03:06:00PM -0400, Tejun Heo wrote:
> Hello,
> 
> On Thu, Jun 19, 2014 at 10:05:49AM -0700, Paul E. McKenney wrote:
> > If you mean what I think you mean by load_acquire_depends(), it is spelled
> > "rcu_dereference()" or, in this case, where you are never removing anything
> > that has been added, "rcu_dereference_raw()".  Because you are never
> > removing anything, you don't need rcu_read_lock() or rcu_read_unlock(),
> > thus you don't want lockdep yelling at you about not having RCU read-side
> > critical sections, thus rcu_dereference_raw().
> 
> Yeah, along that line but it's kinda weird to use rcu_dereference()
> when RCU isn't involved.  It'd be clearer to have something like
> load_acquire_depends() and then define RCU deref in terms of it.
> 
> This is purely notational and clarifiying in the documentation is
> probably enough.

OK.  If there end up being too many non-RCU uses of rcu_dereference_raw(),
then it might make sense to create a new primitive.  But it is not like
we have any shortage of them just now.  ;-)

							Thanx, Paul

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