thermal: core: Introduce thermal_cooling_device_update()

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@intel.com/
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Zhang Rui <rui.zhang@intel.com>
Reviewed-by: Zhang Rui <rui.zhang@intel.com>

1 files changed, 65 insertions, 9 deletions

diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
index cef860deaf91..a4aba7b8bb8b 100644
--- a/drivers/thermal/thermal_sysfs.c
+++ b/drivers/thermal/thermal_sysfs.c
@@ -685,6 +685,8 @@ void thermal_cooling_device_stats_update(struct thermal_cooling_device *cdev,
 {
 	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 device *dev,
 				struct device_attribute *attr, char *buf)
 {
 	struct thermal_cooling_device *cdev = to_cooling_device(dev);
-	struct cooling_dev_stats *stats = cdev->stats;
-	int ret;
+	struct cooling_dev_stats *stats;
+	int ret = 0;
+
+	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, 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;
 
+	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, struct device_attribute *attr,
 	}
 	spin_unlock(&stats->lock);
 
+unlock:
+	mutex_unlock(&cdev->lock);
+
 	return len;
 }
 
@@ -742,8 +763,16 @@ reset_store(struct device *dev, struct device_attribute *attr, const char *buf,
 	    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 device_attribute *attr, const char *buf,
 
 	spin_unlock(&stats->lock);
 
+unlock:
+	mutex_unlock(&cdev->lock);
+
 	return count;
 }
 
@@ -764,10 +796,18 @@ static ssize_t trans_table_show(struct device *dev,
 				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 device *dev,
 			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 device *dev,
 
 	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(struct thermal_cooling_device *cdev)
 	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_sysfs(struct thermal_cooling_device *cdev)
 	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)