From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751905AbaDONR5 (ORCPT ); Tue, 15 Apr 2014 09:17:57 -0400 Received: from merlin.infradead.org ([205.233.59.134]:54906 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750932AbaDONRz (ORCPT ); Tue, 15 Apr 2014 09:17:55 -0400 Date: Tue, 15 Apr 2014 15:17:45 +0200 From: Peter Zijlstra To: "Rafael J. Wysocki" Cc: Nicolas Pitre , Daniel Lezcano , linux-kernel@vger.kernel.org, mingo@elte.hu, linux-pm@vger.kernel.org, alex.shi@linaro.org, vincent.guittot@linaro.org, morten.rasmussen@arm.com Subject: Re: [RFC PATCHC 0/3] sched/idle : find the idlest cpu with cpuidle info Message-ID: <20140415131745.GN11182@twins.programming.kicks-ass.net> References: <1396009796-31598-1-git-send-email-daniel.lezcano@linaro.org> <22904760.5rGZuP5nsx@vostro.rjw.lan> <1930679.LtC4HPqI3x@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1930679.LtC4HPqI3x@vostro.rjw.lan> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.