linux-kernel - Re: [PATCH 0/4] CPUFreq Fixes for 3.9

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Date:	Fri, 8 Feb 2013 10:39:13 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	valdis.kletnieks@...edu, artem.savkov@...il.com,
	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-dev@...ts.linaro.org,
	robin.randhawa@....com, Steve.Bannister@....com,
	Liviu.Dudau@....com, dirk.brandewie@...il.com
Subject: Re: [PATCH 0/4] CPUFreq Fixes for 3.9

On 8 February 2013 04:37, Rafael J. Wysocki <rjw@...k.pl> wrote:
> BTW, there still are locking problems in linux-next.  Why do we need
> to take cpufreq_driver_lock() around driver->init() in cpufreq_add_dev(),
> in particular?

I thought a bit more and realized there is no such limitation on
cpufreq_driver->ops about calling routines which can sleep. And thus
we shoudln't
have locks around any of these. I have got a patch for it, that i
would fold-back into
the original patch that introduced locking fixes (attached too for testing):

From: Viresh Kumar <viresh.kumar@...aro.org>
Date: Fri, 8 Feb 2013 10:35:31 +0530
Subject: [PATCH] cpufreq: Remove unnecessary locking

I have placed some locks intentionally around calls to driver->ops (init/exit),
which look to be wrong as these calls can call routines that potentially sleep.

Lets remove these locks.

Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 drivers/cpufreq/cpufreq.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 5d8a422..04aab05 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -795,10 +795,8 @@ static int cpufreq_add_dev_interface(unsigned int cpu,

 	if (ret) {
 		pr_debug("setting policy failed\n");
-		spin_lock_irqsave(&cpufreq_driver_lock, flags);
 		if (driver->exit)
 			driver->exit(policy);
-		spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
 	}
 	return ret;

@@ -920,17 +918,14 @@ static int cpufreq_add_dev(struct device *dev,
struct subsys_interface *sif)
 	init_completion(&policy->kobj_unregister);
 	INIT_WORK(&policy->update, handle_update);

-	spin_lock_irqsave(&cpufreq_driver_lock, flags);
 	/* call driver. From then on the cpufreq must be able
 	 * to accept all calls to ->verify and ->setpolicy for this CPU
 	 */
 	ret = driver->init(policy);
 	if (ret) {
 		pr_debug("initialization failed\n");
-		spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
 		goto err_set_policy_cpu;
 	}
-	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

 	/* related cpus should atleast have policy->cpus */
 	cpumask_or(policy->related_cpus, policy->related_cpus, policy->cpus);
@@ -1100,10 +1095,8 @@ static int __cpufreq_remove_dev(struct device
*dev, struct subsys_interface *sif
 		wait_for_completion(cmp);
 		pr_debug("wait complete\n");

-		spin_lock_irqsave(&cpufreq_driver_lock, flags);
 		if (driver->exit)
 			driver->exit(data);
-		spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

 		free_cpumask_var(data->related_cpus);
 		free_cpumask_var(data->cpus);

Download attachment "0001-cpufreq-Remove-unnecessary-locking.patch" of type "application/octet-stream" (2230 bytes)