linux-kernel - Re: Locking issues with cpufreq and sysfs

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Date:	Fri, 17 Oct 2014 17:08:29 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	Saravana Kannan <skannan@...eaurora.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Robert Schöne <robert.schoene@...dresden.de>,
	Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: Locking issues with cpufreq and sysfs

On 13 October 2014 18:41, Prarit Bhargava <prarit@...hat.com> wrote:
> There are several issues with the current locking design of cpufreq.  Most
> notably is the panic reported here:
>
> http://marc.info/?l=linux-kernel&m=140622451625236&w=2
>
> which was introduced by commit 955ef4833574636819cd269cfbae12f79cbde63a,
> cpufreq: Drop rwsem lock around CPUFREQ_GOV_POLICY_EXIT, which introduces

Don't know whats going wrong but I am just not able to reproduce the
lockdep again :(
I have tried this on two boards and am making sure that all things are correctly
configured. I am trying this on two of Exynos boards, One a dual-A15 and another
big little with 8 cores..


@@ -2195,9 +2195,7 @@ static int cpufreq_set_policy(struct
cpufreq_policy *policy,
        /* end old governor */
        if (old_gov) {
                __cpufreq_governor(policy, CPUFREQ_GOV_STOP);
-               up_write(&policy->rwsem);
                __cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
-               down_write(&policy->rwsem);
        }

        /* start new governor */
@@ -2206,9 +2204,7 @@ static int cpufreq_set_policy(struct
cpufreq_policy *policy,
                if (!__cpufreq_governor(policy, CPUFREQ_GOV_START))
                        goto out;

-               up_write(&policy->rwsem);
                __cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT);
-               down_write(&policy->rwsem);
        }

diff --git a/drivers/cpufreq/cpufreq_governor.c
b/drivers/cpufreq/cpufreq_governor.c
index 1b44496..1a6972a 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -323,6 +323,7 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                return 0;
        case CPUFREQ_GOV_POLICY_EXIT:
                if (!--dbs_data->usage_count) {
+                       pr_info("%s\n", __func__);
                        sysfs_remove_group(get_governor_parent_kobj(policy),
                                        get_sysfs_attr(dbs_data));




.config attached too, please let me know what am I missing.

Download attachment ".config" of type "application/octet-stream" (74618 bytes)