From mboxrd@z Thu Jan 1 00:00:00 1970 From: Saravana Kannan Subject: Re: [RFC PATCH 11/19] cpufreq: assert policy->rwsem is held in __cpufreq_governor Date: Fri, 29 Jan 2016 16:33:39 -0800 Message-ID: <56AC04E3.8090900@codeaurora.org> References: <1452533760-13787-1-git-send-email-juri.lelli@arm.com> <1452533760-13787-12-git-send-email-juri.lelli@arm.com> <20160112102025.GC1084@ubuntu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160112102025.GC1084@ubuntu> Sender: linux-kernel-owner@vger.kernel.org To: Viresh Kumar Cc: Juri Lelli , 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 List-Id: linux-pm@vger.kernel.org On 01/12/2016 02:20 AM, Viresh Kumar wrote: > On 11-01-16, 17:35, Juri Lelli wrote: >> __cpufreq_governor works on policy, so policy->rwsem has to be held. >> Add assertion for such condition. >> >> 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 f1f9fbc..e7fc5c9 100644 >> --- a/drivers/cpufreq/cpufreq.c >> +++ b/drivers/cpufreq/cpufreq.c >> @@ -1950,6 +1950,9 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, >> /* Don't start any governor operations if we are entering suspend */ >> if (cpufreq_suspended) >> return 0; >> + >> + lockdep_assert_held(&policy->rwsem); >> + > > We had an ABBA problem with the EXIT governor callback and so this > rwsem is dropped just before that from set_policy().. > > commit 955ef4833574 ("cpufreq: Drop rwsem lock around > CPUFREQ_GOV_POLICY_EXIT") > AFAIR, the ABBA issue was between the sysfs lock and the policy lock. The fix for that issue should not be dropping the lock around POLICY_EXIT. The proper fix is to have the governor "export" the attributes it wants to add/remove and have the cpufreq framework do the adding/removing of the attributes from sysfs for the governor. Thanks, Saravana -- Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project