Re: [PATCH v5] PM / devfreq: use _visible attribute to replace create/remove_sysfs_files()

["zhangpengjie (A)" <zhangpengjie2@huawei.com>]

Hi MyungJoo, Kyungmin, and Chanwoo,

Just a gentle ping on this patch.

It has been a while since v5 was submitted, and it seems to have
reached a consensus. It has now collected the following tags:
Reviewed-by: Jonathan Cameron jonathan.cameron@huawei.com
Reviewed-by: Jie Zhan zhanjie9@hisilicon.com
Reviewed-by: Lifeng Zheng zhenglifeng1@huawei.com

Could you please let me know if there are any remaining concerns or if
it can be considered for the next devfreq tree update?

Thanks, Pengjie


On 12/16/2025 11:11 AM, Pengjie Zhang wrote:
> Previously, non-generic attributes (polling_interval, timer) used separate
> create/delete logic, leading to race conditions during concurrent access in
> creation/deletion. Multi-threaded operations also caused inconsistencies
> between governor capabilities and attribute states.
>
> 1.Use is_visible + sysfs_update_group() to unify management of these
> attributes, eliminating creation/deletion races.
> 2.Add locks and validation to these attributes, ensuring consistency
> between current governor capabilities and attribute operations in
> multi-threaded environments.
>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Reviewed-by: Jie Zhan <zhanjie9@hisilicon.com>
> Signed-off-by: Pengjie Zhang <zhangpengjie2@huawei.com>
> ---
> changes in v5:
> -Remove the curly braces of an if statement
> -Added a note explaining why locking is necessary.
> Link to v4:https://lore.kernel.org/all/20251205083724.4068896-1-zhangpengjie2@huawei.com/
>
> changes in v4:
> -Remove the DEFINE_SYSFS_GROUP_VISIBLE macro and directly set the is_visible function.
> -Remove unnecessary ret variables
> Link to v3:https://lore.kernel.org/lkml/20251107031706.1698396-1-zhangpengjie2@huawei.com/
>
> changes in v3:
> - Use guard() to simplify lock acquisition and destruction.
> - Eliminate redundant checks for df.
> Link to v2:https://lore.kernel.org/lkml/20251028022458.2824872-1-zhangpengjie2@huawei.com/
>
> Changes in v2:
> - Fix one problem reported by the kernel test robot.
> - Redirect all error paths in timer_store() to out to ensure locks are not
>   left unReleased.
> Link to v1:https://lore.kernel.org/lkml/20251025135238.3576861-1-zhangpengjie2@huawei.com/
>
>   drivers/devfreq/devfreq.c | 103 ++++++++++++++++++++++----------------
>   1 file changed, 60 insertions(+), 43 deletions(-)
>
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 2e8d01d47f69..7673a39baaa6 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -38,6 +38,7 @@
>   
>   static struct class *devfreq_class;
>   static struct dentry *devfreq_debugfs;
> +static const struct attribute_group gov_attr_group;
>   
>   /*
>    * devfreq core provides delayed work based load monitoring helper
> @@ -785,11 +786,6 @@ static void devfreq_dev_release(struct device *dev)
>   	kfree(devfreq);
>   }
>   
> -static void create_sysfs_files(struct devfreq *devfreq,
> -				const struct devfreq_governor *gov);
> -static void remove_sysfs_files(struct devfreq *devfreq,
> -				const struct devfreq_governor *gov);
> -
>   /**
>    * devfreq_add_device() - Add devfreq feature to the device
>    * @dev:	the device to add devfreq feature.
> @@ -956,7 +952,10 @@ struct devfreq *devfreq_add_device(struct device *dev,
>   			 __func__);
>   		goto err_init;
>   	}
> -	create_sysfs_files(devfreq, devfreq->governor);
> +
> +	err = sysfs_update_group(&devfreq->dev.kobj, &gov_attr_group);
> +	if (err)
> +		goto err_init;
>   
>   	list_add(&devfreq->node, &devfreq_list);
>   
> @@ -995,12 +994,9 @@ int devfreq_remove_device(struct devfreq *devfreq)
>   
>   	devfreq_cooling_unregister(devfreq->cdev);
>   
> -	if (devfreq->governor) {
> +	if (devfreq->governor)
>   		devfreq->governor->event_handler(devfreq,
>   						 DEVFREQ_GOV_STOP, NULL);
> -		remove_sysfs_files(devfreq, devfreq->governor);
> -	}
> -
>   	device_unregister(&devfreq->dev);
>   
>   	return 0;
> @@ -1460,7 +1456,6 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
>   			 __func__, df->governor->name, ret);
>   		goto out;
>   	}
> -	remove_sysfs_files(df, df->governor);
>   
>   	/*
>   	 * Start the new governor and create the specific sysfs files
> @@ -1489,7 +1484,7 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
>   	 * Create the sysfs files for the new governor. But if failed to start
>   	 * the new governor, restore the sysfs files of previous governor.
>   	 */
> -	create_sysfs_files(df, df->governor);
> +	ret = sysfs_update_group(&df->dev.kobj, &gov_attr_group);
>   
>   out:
>   	mutex_unlock(&devfreq_list_lock);
> @@ -1807,14 +1802,17 @@ static struct attribute *devfreq_attrs[] = {
>   	&dev_attr_trans_stat.attr,
>   	NULL,
>   };
> -ATTRIBUTE_GROUPS(devfreq);
>   
>   static ssize_t polling_interval_show(struct device *dev,
>   				     struct device_attribute *attr, char *buf)
>   {
>   	struct devfreq *df = to_devfreq(dev);
>   
> -	if (!df->profile)
> +	/* Protect against race between sysfs attrs update and read/write */
> +	guard(mutex)(&devfreq_list_lock);
> +
> +	if (!df->profile || !df->governor ||
> +	    !IS_SUPPORTED_ATTR(df->governor->attrs, POLLING_INTERVAL))
>   		return -EINVAL;
>   
>   	return sprintf(buf, "%d\n", df->profile->polling_ms);
> @@ -1828,7 +1826,10 @@ static ssize_t polling_interval_store(struct device *dev,
>   	unsigned int value;
>   	int ret;
>   
> -	if (!df->governor)
> +	guard(mutex)(&devfreq_list_lock);
> +
> +	if (!df->governor ||
> +	    !IS_SUPPORTED_ATTR(df->governor->attrs, POLLING_INTERVAL))
>   		return -EINVAL;
>   
>   	ret = sscanf(buf, "%u", &value);
> @@ -1847,7 +1848,10 @@ static ssize_t timer_show(struct device *dev,
>   {
>   	struct devfreq *df = to_devfreq(dev);
>   
> -	if (!df->profile)
> +	guard(mutex)(&devfreq_list_lock);
> +
> +	if (!df->profile || !df->governor ||
> +	    !IS_SUPPORTED_ATTR(df->governor->attrs, TIMER))
>   		return -EINVAL;
>   
>   	return sprintf(buf, "%s\n", timer_name[df->profile->timer]);
> @@ -1861,7 +1865,10 @@ static ssize_t timer_store(struct device *dev, struct device_attribute *attr,
>   	int timer = -1;
>   	int ret = 0, i;
>   
> -	if (!df->governor || !df->profile)
> +	guard(mutex)(&devfreq_list_lock);
> +
> +	if (!df->governor || !df->profile ||
> +	    !IS_SUPPORTED_ATTR(df->governor->attrs, TIMER))
>   		return -EINVAL;
>   
>   	ret = sscanf(buf, "%16s", str_timer);
> @@ -1905,37 +1912,47 @@ static ssize_t timer_store(struct device *dev, struct device_attribute *attr,
>   }
>   static DEVICE_ATTR_RW(timer);
>   
> -#define CREATE_SYSFS_FILE(df, name)					\
> -{									\
> -	int ret;							\
> -	ret = sysfs_create_file(&df->dev.kobj, &dev_attr_##name.attr);	\
> -	if (ret < 0) {							\
> -		dev_warn(&df->dev,					\
> -			"Unable to create attr(%s)\n", "##name");	\
> -	}								\
> -}									\
> +static struct attribute *governor_attrs[] = {
> +	&dev_attr_polling_interval.attr,
> +	&dev_attr_timer.attr,
> +	NULL
> +};
>   
> -/* Create the specific sysfs files which depend on each governor. */
> -static void create_sysfs_files(struct devfreq *devfreq,
> -				const struct devfreq_governor *gov)
> +static umode_t gov_attr_visible(struct kobject *kobj,
> +				struct attribute *attr, int n)
>   {
> -	if (IS_SUPPORTED_ATTR(gov->attrs, POLLING_INTERVAL))
> -		CREATE_SYSFS_FILE(devfreq, polling_interval);
> -	if (IS_SUPPORTED_ATTR(gov->attrs, TIMER))
> -		CREATE_SYSFS_FILE(devfreq, timer);
> -}
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct devfreq *df = to_devfreq(dev);
>   
> -/* Remove the specific sysfs files which depend on each governor. */
> -static void remove_sysfs_files(struct devfreq *devfreq,
> -				const struct devfreq_governor *gov)
> -{
> -	if (IS_SUPPORTED_ATTR(gov->attrs, POLLING_INTERVAL))
> -		sysfs_remove_file(&devfreq->dev.kobj,
> -				&dev_attr_polling_interval.attr);
> -	if (IS_SUPPORTED_ATTR(gov->attrs, TIMER))
> -		sysfs_remove_file(&devfreq->dev.kobj, &dev_attr_timer.attr);
> +	if (!df->governor || !df->governor->attrs)
> +		return 0;
> +
> +	if (attr == &dev_attr_polling_interval.attr &&
> +	    IS_SUPPORTED_ATTR(df->governor->attrs, POLLING_INTERVAL))
> +		return attr->mode;
> +
> +	if (attr == &dev_attr_timer.attr &&
> +	    IS_SUPPORTED_ATTR(df->governor->attrs, TIMER))
> +		return attr->mode;
> +
> +	return 0;
>   }
>   
> +static const struct attribute_group devfreq_group = {
> +	.attrs = devfreq_attrs,
> +};
> +
> +static const struct attribute_group gov_attr_group = {
> +	.attrs = governor_attrs,
> +	.is_visible = gov_attr_visible,
> +};
> +
> +static const struct attribute_group *devfreq_groups[] = {
> +	&devfreq_group,
> +	&gov_attr_group,
> +	NULL
> +};
> +
>   /**
>    * devfreq_summary_show() - Show the summary of the devfreq devices
>    * @s:		seq_file instance to show the summary of devfreq devices