From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934536AbcALLoh (ORCPT ); Tue, 12 Jan 2016 06:44:37 -0500 Received: from foss.arm.com ([217.140.101.70]:33733 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934461AbcALLoc (ORCPT ); Tue, 12 Jan 2016 06:44:32 -0500 Date: Tue, 12 Jan 2016 11:44:54 +0000 From: Juri Lelli To: Viresh Kumar Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, peterz@infradead.org, rjw@rjwysocki.net, mturquette@baylibre.com, steve.muckle@linaro.org, vincent.guittot@linaro.org, morten.rasmussen@arm.com, dietmar.eggemann@arm.com Subject: Re: [RFC PATCH 05/19] cpufreq: assert locking when accessing cpufreq_policy_list Message-ID: <20160112114454.GB7015@e106622-lin> References: <1452533760-13787-1-git-send-email-juri.lelli@arm.com> <1452533760-13787-6-git-send-email-juri.lelli@arm.com> <20160112093452.GW1084@ubuntu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160112093452.GW1084@ubuntu> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 12/01/16 15:04, Viresh Kumar wrote: > On 11-01-16, 17:35, Juri Lelli wrote: > > cpufreq_policy_list is guarded by cpufreq_driver_lock. Add appropriate > > locking assertions to check that we always access the list while holding > > the associated lock. > > > > Cc: "Rafael J. Wysocki" > > Cc: Viresh Kumar > > Signed-off-by: Juri Lelli > > --- > > drivers/cpufreq/cpufreq.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > > index 00a00cd..63d6efb 100644 > > --- a/drivers/cpufreq/cpufreq.c > > +++ b/drivers/cpufreq/cpufreq.c > > @@ -65,6 +65,7 @@ static bool suitable_policy(struct cpufreq_policy *policy, bool active) > > static struct cpufreq_policy *next_policy(struct cpufreq_policy *policy, > > bool active) > > { > > + lockdep_assert_held(&cpufreq_driver_lock); > > do { > > policy = list_next_entry(policy, policy_list); > > > > @@ -80,6 +81,7 @@ static struct cpufreq_policy *first_policy(bool active) > > { > > struct cpufreq_policy *policy; > > > > + lockdep_assert_held(&cpufreq_driver_lock); > > Because both first_policy() and next_policy() are parts of > for_each_suitable_policy() macro, checking this in first_policy() is > sufficient. next_policy() isn't designed to be used by any other code. > But next_policy is called multiple times as part of for_each_suitable_policy(). What if someone thinks she/he can release cpufreq_driver_lock inside for_each_(in)active_policy() loop? Not that it makes sense, but don't you think it could happen? > > /* No policies in the list */ > > if (list_empty(&cpufreq_policy_list)) > > return NULL; > > @@ -2430,6 +2432,7 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data) > > if (ret) > > goto err_boost_unreg; > > > > + lockdep_assert_held(&cpufreq_driver_lock); > > Why do you need a cpufreq_driver_lock here? And the above change > should generate a lockdep here as the lock isn't taken right now. > Because you are checking cpufreq_policy_list to see if it's empty. And it generates a lockdep warning, yes; fixed by next patch. Maybe putting fixes before warnings, as you are suggesting, is better. Thanks, - Juri > > if (!(cpufreq_driver->flags & CPUFREQ_STICKY) && > > list_empty(&cpufreq_policy_list)) { > > /* if all ->init() calls failed, unregister */ > > -- > > 2.2.2 > > -- > viresh >