linux-kernel - Re: [RFC PATCHC 0/3] sched/idle : find the idlest cpu with cpuidle info

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Message-ID: <20140415131745.GN11182@twins.programming.kicks-ass.net>
Date:	Tue, 15 Apr 2014 15:17:45 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu,
	linux-pm@...r.kernel.org, alex.shi@...aro.org,
	vincent.guittot@...aro.org, morten.rasmussen@....com
Subject: Re: [RFC PATCHC 0/3] sched/idle : find the idlest cpu with cpuidle
 info

On Fri, Apr 04, 2014 at 01:43:00PM +0200, Rafael J. Wysocki wrote:
> > We need to ensure the cpuidle data structure is not going away (e.g. 
> > cpuidle driver module removal) while another CPU looks at it though.  
> > The timing would have to be awfully weird for this to happen but still.
> 
> Well, I'm not sure if that is a real concern.  Only a couple of drivers try
> to implement module unloading and I guess this isn't tested too much, so
> perhaps we should just make it impossible to unload a cpuidle driver?

The 'easy' solution is to mandate the use of rcu_read_lock() around the
dereference and make all cpuidle drivers put an rcu_barrier() in their
module unload path.
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