linux-kernel - Re: linux-next 20111025: warnings in rcu_idle_exit_common()/rcu_idle_enter

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Date:	Wed, 02 Nov 2011 10:56:26 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Carsten Emde <cbe@...dl.org>
Subject: Re: linux-next 20111025: warnings in
 rcu_idle_exit_common()/rcu_idle_enter_common()

On Wed, 2011-11-02 at 07:44 -0700, Paul E. McKenney wrote:

> rcu: Fix idle-task checks
> 
> RCU has traditionally relied on idle_cpu() to determine whether a given
> CPU is running in the context of an idle task, but recent changes have
> invalidated this approach.

Correct. idle_cpu() returns if the CPU is idle or not, not if the CPU is
running the idle thread. If the CPU wakes up on the idle thread and
there's tasks on the run queue, then idle_cpu() will return false, even
though the task running is the idle thread. But the CPU itself is not
technically idle.

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve




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