Re: [PATCH v1 3/4] thermal: core: Introduce thermal_cooling_device_update()

[Zhang, Rui]

On Fri, 2023-03-03 at 20:23 +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> 
> Introduce a core thermal API function,
> thermal_cooling_device_update(),
> for updating the max_state value for a cooling device and rearranging
> its statistics in sysfs after a possible change of its
> ->get_max_state()
> callback return value.
> 
> That callback is now invoked only once, during cooling device
> registration, to populate the max_state field in the cooling device
> object, so if its return value changes, it needs to be invoked again
> and the new return value needs to be stored as max_state.  Moreover,
> the statistics presented in sysfs need to be rearranged in general,
> because there may not be enough room in them to store data for all
> of the possible states (in the case when max_state grows).
> 
> The new function takes care of that (and some other minor things
> related to it), but some extra locking and lockdep annotations are
> added in several places too to protect against crashes in the cases
> when the statistics are not present or when a stale max_state value
> might be used by sysfs attributes.
> 
> Note that the actual user of the new function will be added
> separately.
> 
> Link: 
> https://lore.kernel.org/linux-pm/53ec1f06f61c984100868926f282647e57ecfb2d.camel@xxxxxxxxx/
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
>  drivers/thermal/thermal_core.c  |   47 ++++++++++++++++++++++++++
>  drivers/thermal/thermal_core.h  |    1 
>  drivers/thermal/thermal_sysfs.c |   72
> +++++++++++++++++++++++++++++++++++-----
>  include/linux/thermal.h         |    1 
>  4 files changed, 113 insertions(+), 8 deletions(-)
> 
> Index: linux-pm/drivers/thermal/thermal_core.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_core.c
> +++ linux-pm/drivers/thermal/thermal_core.c
> @@ -1057,6 +1057,53 @@ static bool thermal_cooling_device_prese
>  	return false;
>  }
>  
> +void thermal_cooling_device_update(struct thermal_cooling_device
> *cdev)
> +{
> +	unsigned long state;
> +
> +	if (!cdev)
> +		return;
> +
> +	/*
> +	 * Hold thermal_list_lock throughout the update to prevent the
> device
> +	 * from going away while being updated.
> +	 */
> +	mutex_lock(&thermal_list_lock);
> +
> +	if (!thermal_cooling_device_present(cdev))
> +		goto unlock_list;
> +
> +	/*
> +	 * Update under the cdev lock to prevent the state from being
> set beyond
> +	 * the new limit concurrently.
> +	 */
> +	mutex_lock(&cdev->lock);
> +
> +	if (cdev->ops->get_max_state(cdev, &cdev->max_state))
> +		goto unlock;
> +
> +	thermal_cooling_device_stats_reinit(cdev);
> +
> +	if (cdev->ops->get_cur_state(cdev, &state))
> +		goto unlock;
> +
> +	if (state <= cdev->max_state)
> +		goto update_stats;
> +
how could the .get_cur_state() callback returns a value higher than
.get_max_state()? Isn't this a driver problem?

> +	if (cdev->ops->set_cur_state(cdev, state))
> +		goto unlock;

even if we don't error out, should we reevaluate .get_max_state() and
update cdev->max_state?

thanks,
rui
> +
> +update_stats:
> +	thermal_cooling_device_stats_update(cdev, state);
> +
> +unlock:
> +	mutex_unlock(&cdev->lock);
> +
> +unlock_list:
> +	mutex_unlock(&thermal_list_lock);
> +}
> +EXPORT_SYMBOL_GPL(thermal_cooling_device_update);
> +
>  static void __unbind(struct thermal_zone_device *tz, int mask,
>  		     struct thermal_cooling_device *cdev)
>  {
> Index: linux-pm/drivers/thermal/thermal_sysfs.c
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_sysfs.c
> +++ linux-pm/drivers/thermal/thermal_sysfs.c
> @@ -685,6 +685,8 @@ void thermal_cooling_device_stats_update
>  {
>  	struct cooling_dev_stats *stats = cdev->stats;
>  
> +	lockdep_assert_held(&cdev->lock);
> +
>  	if (!stats)
>  		return;
>  
> @@ -706,13 +708,22 @@ static ssize_t total_trans_show(struct d
>  				struct device_attribute *attr, char
> *buf)
>  {
>  	struct thermal_cooling_device *cdev = to_cooling_device(dev);
> -	struct cooling_dev_stats *stats = cdev->stats;
> +	struct cooling_dev_stats *stats;
>  	int ret;
>  
> +	mutex_lock(&cdev->lock);
> +
> +	stats = cdev->stats;
> +	if (!stats)
> +		goto unlock;
> +
>  	spin_lock(&stats->lock);
>  	ret = sprintf(buf, "%u\n", stats->total_trans);
>  	spin_unlock(&stats->lock);
>  
> +unlock:
> +	mutex_unlock(&cdev->lock);
> +
>  	return ret;
>  }
>  
> @@ -721,11 +732,18 @@ time_in_state_ms_show(struct device *dev
>  		      char *buf)
>  {
>  	struct thermal_cooling_device *cdev = to_cooling_device(dev);
> -	struct cooling_dev_stats *stats = cdev->stats;
> +	struct cooling_dev_stats *stats;
>  	ssize_t len = 0;
>  	int i;
>  
> +	mutex_lock(&cdev->lock);
> +
> +	stats = cdev->stats;
> +	if (!stats)
> +		goto unlock;
> +
>  	spin_lock(&stats->lock);
> +
>  	update_time_in_state(stats);
>  
>  	for (i = 0; i <= cdev->max_state; i++) {
> @@ -734,6 +752,9 @@ time_in_state_ms_show(struct device *dev
>  	}
>  	spin_unlock(&stats->lock);
>  
> +unlock:
> +	mutex_unlock(&cdev->lock);
> +
>  	return len;
>  }
>  
> @@ -742,8 +763,16 @@ reset_store(struct device *dev, struct d
>  	    size_t count)
>  {
>  	struct thermal_cooling_device *cdev = to_cooling_device(dev);
> -	struct cooling_dev_stats *stats = cdev->stats;
> -	int i, states = cdev->max_state + 1;
> +	struct cooling_dev_stats *stats;
> +	int i, states;
> +
> +	mutex_lock(&cdev->lock);
> +
> +	stats = cdev->stats;
> +	if (!stats)
> +		goto unlock;
> +
> +	states = cdev->max_state + 1;
>  
>  	spin_lock(&stats->lock);
>  
> @@ -757,6 +786,9 @@ reset_store(struct device *dev, struct d
>  
>  	spin_unlock(&stats->lock);
>  
> +unlock:
> +	mutex_unlock(&cdev->lock);
> +
>  	return count;
>  }
>  
> @@ -764,10 +796,18 @@ static ssize_t trans_table_show(struct d
>  				struct device_attribute *attr, char
> *buf)
>  {
>  	struct thermal_cooling_device *cdev = to_cooling_device(dev);
> -	struct cooling_dev_stats *stats = cdev->stats;
> +	struct cooling_dev_stats *stats;
>  	ssize_t len = 0;
>  	int i, j;
>  
> +	mutex_lock(&cdev->lock);
> +
> +	stats = cdev->stats;
> +	if (!stats) {
> +		len = -ENODATA;
> +		goto unlock;
> +	}
> +
>  	len += snprintf(buf + len, PAGE_SIZE - len, "
> From  :    To\n");
>  	len += snprintf(buf + len, PAGE_SIZE - len, "       : ");
>  	for (i = 0; i <= cdev->max_state; i++) {
> @@ -775,8 +815,10 @@ static ssize_t trans_table_show(struct d
>  			break;
>  		len += snprintf(buf + len, PAGE_SIZE - len,
> "state%2u  ", i);
>  	}
> -	if (len >= PAGE_SIZE)
> -		return PAGE_SIZE;
> +	if (len >= PAGE_SIZE) {
> +		len = PAGE_SIZE;
> +		goto unlock;
> +	}
>  
>  	len += snprintf(buf + len, PAGE_SIZE - len, "\n");
>  
> @@ -799,8 +841,12 @@ static ssize_t trans_table_show(struct d
>  
>  	if (len >= PAGE_SIZE) {
>  		pr_warn_once("Thermal transition table exceeds
> PAGE_SIZE. Disabling\n");
> -		return -EFBIG;
> +		len = -EFBIG;
>  	}
> +
> +unlock:
> +	mutex_unlock(&cdev->lock);
> +
>  	return len;
>  }
>  
> @@ -830,6 +876,8 @@ static void cooling_device_stats_setup(s
>  	unsigned long states = cdev->max_state + 1;
>  	int var;
>  
> +	lockdep_assert_held(&cdev->lock);
> +
>  	var = sizeof(*stats);
>  	var += sizeof(*stats->time_in_state) * states;
>  	var += sizeof(*stats->trans_table) * states * states;
> @@ -855,6 +903,8 @@ out:
>  
>  static void cooling_device_stats_destroy(struct
> thermal_cooling_device *cdev)
>  {
> +	lockdep_assert_held(&cdev->lock);
> +
>  	kfree(cdev->stats);
>  	cdev->stats = NULL;
>  }
> @@ -879,6 +929,12 @@ void thermal_cooling_device_destroy_sysf
>  	cooling_device_stats_destroy(cdev);
>  }
>  
> +void thermal_cooling_device_stats_reinit(struct
> thermal_cooling_device *cdev)
> +{
> +	cooling_device_stats_destroy(cdev);
> +	cooling_device_stats_setup(cdev);
> +}
> +
>  /* these helper will be used only at the time of bindig */
>  ssize_t
>  trip_point_show(struct device *dev, struct device_attribute *attr,
> char *buf)
> Index: linux-pm/drivers/thermal/thermal_core.h
> ===================================================================
> --- linux-pm.orig/drivers/thermal/thermal_core.h
> +++ linux-pm/drivers/thermal/thermal_core.h
> @@ -127,6 +127,7 @@ int thermal_zone_create_device_groups(st
>  void thermal_zone_destroy_device_groups(struct thermal_zone_device
> *);
>  void thermal_cooling_device_setup_sysfs(struct
> thermal_cooling_device *);
>  void thermal_cooling_device_destroy_sysfs(struct
> thermal_cooling_device *cdev);
> +void thermal_cooling_device_stats_reinit(struct
> thermal_cooling_device *cdev);
>  /* used only at binding time */
>  ssize_t trip_point_show(struct device *, struct device_attribute *,
> char *);
>  ssize_t weight_show(struct device *, struct device_attribute *, char
> *);
> Index: linux-pm/include/linux/thermal.h
> ===================================================================
> --- linux-pm.orig/include/linux/thermal.h
> +++ linux-pm/include/linux/thermal.h
> @@ -384,6 +384,7 @@ devm_thermal_of_cooling_device_register(
>  				struct device_node *np,
>  				char *type, void *devdata,
>  				const struct thermal_cooling_device_ops
> *ops);
> +void thermal_cooling_device_update(struct thermal_cooling_device *);
>  void thermal_cooling_device_unregister(struct thermal_cooling_device
> *);
>  struct thermal_zone_device *thermal_zone_get_zone_by_name(const char
> *name);
>  int thermal_zone_get_temp(struct thermal_zone_device *tz, int
> *temp);
> 
> 
>