From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755260AbaHFKJx (ORCPT ); Wed, 6 Aug 2014 06:09:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52152 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753286AbaHFKJv (ORCPT ); Wed, 6 Aug 2014 06:09:51 -0400 Message-ID: <53E1FEE5.80305@redhat.com> Date: Wed, 06 Aug 2014 06:09:41 -0400 From: Prarit Bhargava User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20131028 Thunderbird/17.0.10 MIME-Version: 1.0 To: Viresh Kumar CC: Saravana Kannan , Stephen Boyd , "Rafael J. Wysocki" , Linux Kernel Mailing List , Lenny Szubowicz , "linux-pm@vger.kernel.org" Subject: Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2] References: <1406634362-811-1-git-send-email-prarit@redhat.com> <2066166.pXm4lKLOID@vostro.rjw.lan> <53DA8389.80804@redhat.com> <1917362.abr2Y4p7vh@vostro.rjw.lan> <53DA8A41.2030601@redhat.com> <53DAA60B.6040802@codeaurora.org> <53DAA749.5080506@redhat.com> <53DAA95B.2040505@codeaurora.org> <53DAB038.3050007@redhat.com> <53DABFA6.6090503@codeaurora.org> <53DACA26.1000908@redhat.com> <53DAE592.2030909@codeaurora.org> <53DB6B81.6050400@redhat.com> <53DBCBE8.6010809@codeaurora.org> <53DBE764.8050109@redhat.com> <53DBEC27.7050803@codeaurora.org> <53E0B657.4070007@redhat.com> <53E1556B.5070304@codeaurora.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/06/2014 04:10 AM, Viresh Kumar wrote: > On 6 August 2014 03:36, Saravana Kannan wrote: >> Stephen and I looked into this. This is not a sysfs framework difference. >> The reason we don't have this issue when we use global tunables is because >> we add the attribute group to the cpufreq_global_kobject and that kobject >> doesn't have a kobj_type ops similar to the per policy kobject. So, >> read/write to those attributes do NOT go through the generic show/store ops >> that wrap every other cpufreq framework attribute read/writes. >> >> So, none of those read/write do any kind of locking. They don't race with >> POLICY_EXIT (because we remove the sysfs group first thing in POLICY_EXIT) >> but might still race with START/STOPs (not sure, haven't looked closely >> yet). >> >> For example, writing to sampling_rate of ondemand governor might cause a >> race in update_sampling_rate(). It could race and happen between a STOP and >> POLICY_EXIT (triggered by hotplug, gov change, etc). > > This sounds good but I couldn't prove it. Doing this on my dual core exynos > doesn't give me that crash report and it should? Are you sure you're not seeing another lockdep warning? That was my problem -- there was an xfs related lockdep warning which then resulted in lockdep being disabled from that point on. P. > > diff --git a/drivers/cpufreq/exynos-cpufreq.c b/drivers/cpufreq/exynos-cpufreq.c > index 1e0ec57..027b6f7 100644 > --- a/drivers/cpufreq/exynos-cpufreq.c > +++ b/drivers/cpufreq/exynos-cpufreq.c > @@ -139,7 +139,7 @@ static int exynos_cpufreq_cpu_init(struct > cpufreq_policy *policy) > } > > static struct cpufreq_driver exynos_driver = { > - .flags = CPUFREQ_STICKY | CPUFREQ_NEED_INITIAL_FREQ_CHECK, > + .flags = CPUFREQ_STICKY | > CPUFREQ_NEED_INITIAL_FREQ_CHECK | CPUFREQ_HAVE_GOVERNOR_PER_POLICY, > .verify = cpufreq_generic_frequency_table_verify, > .target_index = exynos_target, > .get = cpufreq_generic_get, >