Re: [PATCH v3 1/3] PM / OPP: add dev_pm_opp_get_suspend_opp() helper

[Viresh Kumar]

On 03-09-15, 20:11, Bartlomiej Zolnierkiewicz wrote:
> Add dev_pm_opp_get_suspend_opp() helper to obtain suspend opp.
> 
> Cc: Viresh Kumar 
> Cc: Thomas Abraham 
> Cc: Javier Martinez Canillas 
> Cc: Krzysztof Kozlowski 
> Cc: Marek Szyprowski 
> Cc: Tobias Jakobi 
> Signed-off-by: Bartlomiej Zolnierkiewicz 
> ---
>  drivers/base/power/opp.c | 28 
>  include/linux/pm_opp.h   |  6 ++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
> index eb25449..eaafca7 100644
> --- a/drivers/base/power/opp.c
> +++ b/drivers/base/power/opp.c
> @@ -341,6 +341,34 @@ unsigned long dev_pm_opp_get_max_clock_latency(struct 
> device *dev)
>  EXPORT_SYMBOL_GPL(dev_pm_opp_get_max_clock_latency);
>  
>  /**
> + * dev_pm_opp_get_suspend_opp() - Get suspend opp
> + * @dev: device for which we do this operation
> + *
> + * Return: This function returns pointer to the suspend opp if it is
> + * defined, otherwise it returns NULL.
> + *
> + * Locking: This function takes rcu_read_lock().
> + */
> +struct dev_pm_opp *dev_pm_opp_get_suspend_opp(struct device *dev)
> +{
> + struct device_opp *dev_opp;
> + struct dev_pm_opp *suspend_opp;
> +
> + rcu_read_lock();

This is wrong. Please have a look at other exported APIs that return
an OPP. RCU protected structures must be accessed from within RCU
locks _ONLY_. But your function returns the pointer after dropping
the locks. Which essentially means that the OPP can be freed by core,
by the time you start using it. :)

So, in such cases, its upto the caller to ensure that locks are taken
properly.

You can look at dev_pm_opp_find_freq_exact() as an example.

-- 
viresh
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[PATCH v3 1/3] PM / OPP: add dev_pm_opp_get_suspend_opp() helper

[Bartlomiej Zolnierkiewicz]

Add dev_pm_opp_get_suspend_opp() helper to obtain suspend opp.

Cc: Viresh Kumar 
Cc: Thomas Abraham 
Cc: Javier Martinez Canillas 
Cc: Krzysztof Kozlowski 
Cc: Marek Szyprowski 
Cc: Tobias Jakobi 
Signed-off-by: Bartlomiej Zolnierkiewicz 
---
 drivers/base/power/opp.c | 28 
 include/linux/pm_opp.h   |  6 ++
 2 files changed, 34 insertions(+)

diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
index eb25449..eaafca7 100644
--- a/drivers/base/power/opp.c
+++ b/drivers/base/power/opp.c
@@ -341,6 +341,34 @@ unsigned long dev_pm_opp_get_max_clock_latency(struct 
device *dev)
 EXPORT_SYMBOL_GPL(dev_pm_opp_get_max_clock_latency);
 
 /**
+ * dev_pm_opp_get_suspend_opp() - Get suspend opp
+ * @dev:   device for which we do this operation
+ *
+ * Return: This function returns pointer to the suspend opp if it is
+ * defined, otherwise it returns NULL.
+ *
+ * Locking: This function takes rcu_read_lock().
+ */
+struct dev_pm_opp *dev_pm_opp_get_suspend_opp(struct device *dev)
+{
+   struct device_opp *dev_opp;
+   struct dev_pm_opp *suspend_opp;
+
+   rcu_read_lock();
+
+   dev_opp = _find_device_opp(dev);
+   if (IS_ERR(dev_opp))
+   suspend_opp = NULL;
+   else
+   suspend_opp = dev_opp->suspend_opp;
+
+   rcu_read_unlock();
+
+   return suspend_opp;
+}
+EXPORT_SYMBOL_GPL(dev_pm_opp_get_suspend_opp);
+
+/**
  * dev_pm_opp_get_opp_count() - Get number of opps available in the opp list
  * @dev:   device for which we do this operation
  *
diff --git a/include/linux/pm_opp.h b/include/linux/pm_opp.h
index cab7ba5..e817722 100644
--- a/include/linux/pm_opp.h
+++ b/include/linux/pm_opp.h
@@ -34,6 +34,7 @@ bool dev_pm_opp_is_turbo(struct dev_pm_opp *opp);
 
 int dev_pm_opp_get_opp_count(struct device *dev);
 unsigned long dev_pm_opp_get_max_clock_latency(struct device *dev);
+struct dev_pm_opp *dev_pm_opp_get_suspend_opp(struct device *dev);
 
 struct dev_pm_opp *dev_pm_opp_find_freq_exact(struct device *dev,
  unsigned long freq,
@@ -80,6 +81,11 @@ static inline unsigned long 
dev_pm_opp_get_max_clock_latency(struct device *dev)
return 0;
 }
 
+static inline struct dev_pm_opp *dev_pm_opp_get_suspend_opp(struct device *dev)
+{
+   return NULL;
+}
+
 static inline struct dev_pm_opp *dev_pm_opp_find_freq_exact(struct device *dev,
unsigned long freq, bool available)
 {
-- 
1.9.1

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