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

[Viresh Kumar]

On 8 February 2013 04:37, Rafael J. Wysocki <r...@sisk.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.ku...@linaro.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.ku...@linaro.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);

0001-cpufreq-Remove-unnecessary-locking.patch
Description: Binary data