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Date: Thu, 10 Nov 2011 09:20:30 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@elte.hu>, Lai Jiangshan <laijs@cn.fujitsu.com>,
        Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: linux-next 20111025: warnings in
 rcu_idle_exit_common()/rcu_idle_enter_common()
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On Thu, Nov 10, 2011 at 05:35:24PM +0100, Peter Zijlstra wrote:
> On Mon, 2011-10-31 at 15:14 -0700, Paul E. McKenney wrote:
> > Peter, I have been using "idle_cpu(smp_processor_id()))" to verify that
> > I really am running in the context of the idle task when RCU believes
> > that the current CPU has gone idle. 
> 
> I think this is sorted since, but just to clarify idle_cpu() was meant
> to test if the cpu was idle, this is something different from actually
> running the idle thread.

Thank you, and yes, looks like the ->pid==0 approach works well.

Should this be encapsulated, for example in an inline function something
as follows?

static inline void cpu_is_running_idle_task(struct task_struct *tsk)
{
	return tsk->pid == 0;
}

I am sure I could come up with a longer name, if you would prefer.  ;-)

I would be happy to create the patch and fix up the other open-coded
uses of ->pid==0 if this approach looks good to you.

							Thanx, Paul