linux-kernel - Re: [PATCH percpu/for-3.11] percpu-refcount: consistently use plain (non-sched) RCU

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Message-ID: <20130612205500.GE6151@google.com>
Date:	Wed, 12 Jun 2013 13:55:00 -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 percpu/for-3.11] percpu-refcount: consistently use plain
 (non-sched) RCU

On Wed, Jun 12, 2013 at 01:40:32PM -0700, Tejun Heo wrote:
> From e96262150a513ce3d54ff221d4ace8aeec96e0bf Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@...nel.org>
> Date: Wed, 12 Jun 2013 13:37:42 -0700
> 
> percpu_ref_get/put() are using preempt_disable/enable() while
> percpu_ref_kill() is using plain call_rcu() instead of
> call_rcu_sched().  This is buggy as grace periods of the two may not
> match.  Fix it by using plain RCU in percpu_ref_get/put().
> 
> (I suggested using sched RCU in the first place but there's no actual
>  benefit in doing so unless we're gonna introduce different variants
>  of get/put to be called while preemption is alredy disabled, which we
>  definitely shouldn't.)
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Rusty Russell <rusty@...tcorp.com.au>

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