linux-kernel - Re: [PATCH 2/2] percpu-refcount: implement percpu_tryget() along with percpu_ref_kill_and

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Message-ID: <20130613234459.GE28664@moria.home.lan>
Date:	Thu, 13 Jun 2013 16:44:59 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Tejun Heo <theo@...hat.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 2/2] percpu-refcount: implement percpu_tryget() along
 with percpu_ref_kill_and_confirm()

On Wed, Jun 12, 2013 at 01:46:27PM -0700, Tejun Heo wrote:
> From de3c0749e2c1960afcc433fc5da136b85c8bd896 Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@...nel.org>
> Date: Wed, 12 Jun 2013 13:37:42 -0700
> 
> Implement percpu_tryget() which succeeds iff the refcount hasn't been
> killed yet.  Because the refcnt is per-cpu, different CPUs may have
> different perceptions on when the counter has been killed and tryget()
> may continue to succeed for a while after percpu_ref_kill() returns.
> 
> For use cases where it's necessary to know when all CPUs start to see
> the refcnt as dead, percpu_ref_kill_and_confirm() is added.  The new
> function takes an extra argument @confirm_kill which is invoked when
> the refcnt is guaranteed to be viewed as killed on all CPUs.
> 
> While this isn't the prettiest interface, it doesn't force synchronous
> wait and is much safer than requiring the caller to do its own
> call_rcu().
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>

Acked-by: Kent Overstreet <koverstreet@...gle.com>
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