[PATCH] thermal: Fix locking in cooling device sysfs update cur_state

[PATCH] thermal: Fix locking in cooling device sysfs update cur_state

[Thara Gopinath]

Sysfs interface to update cooling device cur_state does not
currently hold cooling device lock, leading to stale values
in cur_state especially if getting updated simultanelously
from user space and thermal framework. Adding the proper locking
code fixes this issue.

Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
---
 drivers/thermal/thermal_sysfs.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
index 2241cea..1f0c1e2 100644
--- a/drivers/thermal/thermal_sysfs.c
+++ b/drivers/thermal/thermal_sysfs.c
@@ -712,10 +712,14 @@ cur_state_store(struct device *dev, struct device_attribute *attr,
 	if ((long)state < 0)
 		return -EINVAL;
 
+	mutex_lock(&cdev->lock);
 	result = cdev->ops->set_cur_state(cdev, state);
-	if (result)
+	if (result) {
+		mutex_unlock(&cdev->lock);
 		return result;
+	}
 	thermal_cooling_device_stats_update(cdev, state);
+	mutex_unlock(&cdev->lock);
 	return count;
 }
 
-- 
2.1.4

Re: [PATCH] thermal: Fix locking in cooling device sysfs update cur_state

[Daniel Lezcano]

On 21/11/2018 20:01, Thara Gopinath wrote:
> Sysfs interface to update cooling device cur_state does not
> currently hold cooling device lock, leading to stale values
> in cur_state especially if getting updated simultanelously
> from user space and thermal framework. Adding the proper locking
> code fixes this issue.
>
> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
> ---
>  drivers/thermal/thermal_sysfs.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> index 2241cea..1f0c1e2 100644
> --- a/drivers/thermal/thermal_sysfs.c
> +++ b/drivers/thermal/thermal_sysfs.c
> @@ -712,10 +712,14 @@ cur_state_store(struct device *dev, struct device_attribute *attr,
>  	if ((long)state < 0)
>  		return -EINVAL;
>  
> +	mutex_lock(&cdev->lock);
>  	result = cdev->ops->set_cur_state(cdev, state);
> -	if (result)
> +	if (result) {
> +		mutex_unlock(&cdev->lock);
>  		return result;
> +	}
>  	thermal_cooling_device_stats_update(cdev, state);
> +	mutex_unlock(&cdev->lock);

I suggest to invert the condition:

	mutex_lock(&cdev->lock);
	result = cdev->ops->set_cur_state(cdev, state);
	if (!result)
		thermal_cooling_device_stats_update(cdev, state);
	mutex_unlock(&cdev->lock);

	return result ? result : count;


The same problem is there for the cur_state_show() callback.

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