linux-kernel - Re: [PATCH percpu/for-3.11 2/2] percpu-refcount: implement percpu_ref_cancel

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Date:	Wed, 12 Jun 2013 20:58:31 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Oleg Nesterov <oleg@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH percpu/for-3.11 2/2] percpu-refcount: implement
 percpu_ref_cancel_init()

On Wed, Jun 12, 2013 at 08:56:36PM -0700, Kent Overstreet wrote:
> On Wed, Jun 12, 2013 at 08:52:35PM -0700, Tejun Heo wrote:
> > Normally, percpu_ref_init() initializes and percpu_ref_kill*()
> > initiates destruction which completes asynchronously.  The
> > asynchronous destruction can be problematic in init failure path where
> > the caller wants to destroy half-constructed object - distinguishing
> > half-constructed objects from the usual release method can be painful
> > for complex objects.
> > 
> > This patch implements percpu_ref_cancel_init() which synchronously
> > destroys the percpu_ref without invoking release.  To avoid
> > unintentional misuses, the function requires the ref to have finished
> > percpu_ref_init() but never used and triggers WARN otherwise.
> 
> That's a good idea, I should've implemented that for aio.
> 
> I probably would've just gone with percpu_ref_free() (if caller knows
> it's safe, they can do whatever they want) but I suppose I can live with
> percpu_ref_cancel_init().

At first I named it percpu_ref_free() but it looked too symmetric to
init, more so than kill, so I was worried that people might get
confused that this is the normal interface to shutdown a percpu
refcnt, so the weird cancel_init name and further restriction on its
usage.

Thanks.

-- 
tejun
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