[13/13] cpufreq: make sure frequency transitions are serialized

Message ID 0bebf56a27f799a282cc00d0c17c187f9941f122.1371630975.git.viresh.kumar@linaro.org
State Accepted
Headers show

Commit Message

Viresh Kumar June 19, 2013, 8:53 a.m.
Whenever we are changing frequency of a cpu, we are calling PRECHANGE and
POSTCHANGE notifiers. They must be serialized. i.e. PRECHANGE or POSTCHANGE
shouldn't be called twice contiguously.

This can happen due to bugs in users of __cpufreq_driver_target() or actual
cpufreq drivers who are sending these notifiers.

This patch adds some protection against this. Now, we keep track of the last
transaction and see if something went wrong.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 drivers/cpufreq/cpufreq.c | 9 +++++++++
 1 file changed, 9 insertions(+)

Comments

Rafael J. Wysocki June 24, 2013, 11:43 a.m. | #1
On Wednesday, June 19, 2013 02:23:07 PM Viresh Kumar wrote:
> Whenever we are changing frequency of a cpu, we are calling PRECHANGE and
> POSTCHANGE notifiers. They must be serialized. i.e. PRECHANGE or POSTCHANGE
> shouldn't be called twice contiguously.
> 
> This can happen due to bugs in users of __cpufreq_driver_target() or actual
> cpufreq drivers who are sending these notifiers.
> 
> This patch adds some protection against this. Now, we keep track of the last
> transaction and see if something went wrong.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
>  drivers/cpufreq/cpufreq.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 2d53f47..92cb8b3 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -107,6 +107,9 @@ static void handle_update(struct work_struct *work);
>  static BLOCKING_NOTIFIER_HEAD(cpufreq_policy_notifier_list);
>  static struct srcu_notifier_head cpufreq_transition_notifier_list;
>  
> +/* Tracks status of transition */
> +static int transition_ongoing;
> +
>  static bool init_cpufreq_transition_notifier_list_called;
>  static int __init init_cpufreq_transition_notifier_list(void)
>  {
> @@ -264,6 +267,8 @@ void __cpufreq_notify_transition(struct cpufreq_policy *policy,
>  	switch (state) {
>  
>  	case CPUFREQ_PRECHANGE:
> +		WARN_ON(transition_ongoing++);
> +
>  		/* detect if the driver reported a value as "old frequency"
>  		 * which is not equal to what the cpufreq core thinks is
>  		 * "old frequency".
> @@ -283,6 +288,8 @@ void __cpufreq_notify_transition(struct cpufreq_policy *policy,
>  		break;
>  
>  	case CPUFREQ_POSTCHANGE:
> +		WARN_ON(!transition_ongoing--);

Shouldn't we try to avoid going into the negative range here?

> +
>  		adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
>  		pr_debug("FREQ: %lu - CPU: %lu", (unsigned long)freqs->new,
>  			(unsigned long)freqs->cpu);
> @@ -1458,6 +1465,8 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy,
>  
>  	if (cpufreq_disabled())
>  		return -ENODEV;
> +	if (transition_ongoing)
> +		return -EBUSY;
>  
>  	/* Make sure that target_freq is within supported range */
>  	if (target_freq > policy->max)
> 

Rafael

Patch

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 2d53f47..92cb8b3 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -107,6 +107,9 @@  static void handle_update(struct work_struct *work);
 static BLOCKING_NOTIFIER_HEAD(cpufreq_policy_notifier_list);
 static struct srcu_notifier_head cpufreq_transition_notifier_list;
 
+/* Tracks status of transition */
+static int transition_ongoing;
+
 static bool init_cpufreq_transition_notifier_list_called;
 static int __init init_cpufreq_transition_notifier_list(void)
 {
@@ -264,6 +267,8 @@  void __cpufreq_notify_transition(struct cpufreq_policy *policy,
 	switch (state) {
 
 	case CPUFREQ_PRECHANGE:
+		WARN_ON(transition_ongoing++);
+
 		/* detect if the driver reported a value as "old frequency"
 		 * which is not equal to what the cpufreq core thinks is
 		 * "old frequency".
@@ -283,6 +288,8 @@  void __cpufreq_notify_transition(struct cpufreq_policy *policy,
 		break;
 
 	case CPUFREQ_POSTCHANGE:
+		WARN_ON(!transition_ongoing--);
+
 		adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
 		pr_debug("FREQ: %lu - CPU: %lu", (unsigned long)freqs->new,
 			(unsigned long)freqs->cpu);
@@ -1458,6 +1465,8 @@  int __cpufreq_driver_target(struct cpufreq_policy *policy,
 
 	if (cpufreq_disabled())
 		return -ENODEV;
+	if (transition_ongoing)
+		return -EBUSY;
 
 	/* Make sure that target_freq is within supported range */
 	if (target_freq > policy->max)