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Commit 0ea57b93 authored by Ram Chandrasekar's avatar Ram Chandrasekar Committed by Gerrit - the friendly Code Review server
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thermal-core: Use rcu when accessing threshold list 



Threshold list will be read in interrupt context. Using
a lock in the interrupt context is not acceptable, but the
list traversal needs to be protected. Because the threshold
list can be updated with a new threshold or an existing
threshold can be removed. Doing a list traversal during the
list mutation may result in unassigned memory access
violation. Use of list_for_each_entry_safe() function for
traversing, won't help. Because this function can help
only if the traversal loop removes the current element, that
is pointed by this iteration.

Use rcu to ensure a safe list traversal without a lock.
Addition or deletion to the threshold list is an infrequent
operation when compared to the threshold list read, which
happens when temperature threshold trips. Using rcu ensures
that read operations are done faster without getting
blocked by a lock and the list write operations are done
in a list safe fashion. Replace the list_for_each_entry_safe()
function with rcu safe list traversal function
list_for_each_entry_rcu(), wherever it is applicable.

Change-Id: I7636711bfc6bd63fe3adaad38a5471e3508e240b
Signed-off-by: default avatarRam Chandrasekar <rkumbako@codeaurora.org>
parent 1acad2bb

drivers/thermal/thermal_core.c

+12 −10
Original line number Diff line number Diff line
@@ -273,7 +273,7 @@ static int __update_sensor_thresholds(struct sensor_info *sensor) 
{

	long max_of_low_thresh = LONG_MIN;

	long min_of_high_thresh = LONG_MAX;

	struct sensor_threshold *pos, *var;

	struct sensor_threshold *pos = NULL;

	int ret = 0;



	if (!sensor->tz->ops->set_trip_temp ||
@@ -287,7 +287,7 @@ static int __update_sensor_thresholds(struct sensor_info *sensor) 
	if ((sensor->max_idx == -1) || (sensor->min_idx == -1))

		init_sensor_trip(sensor);



	list_for_each_entry_safe(pos, var, &sensor->threshold_list, list) {

	list_for_each_entry(pos, &sensor->threshold_list, list) {

		if (!pos->active)

			continue;

		if (pos->trip == THERMAL_TRIP_CONFIGURABLE_LOW) {
@@ -389,7 +389,7 @@ static __ref int sensor_sysfs_notify(void *data) 
int thermal_sensor_trip(struct thermal_zone_device *tz,

		enum thermal_trip_type trip, long temp)

{

	struct sensor_threshold *pos, *var;

	struct sensor_threshold *pos = NULL;

	int ret = -ENODEV;



	if (trip != THERMAL_TRIP_CONFIGURABLE_HI &&
@@ -399,7 +399,8 @@ int thermal_sensor_trip(struct thermal_zone_device *tz, 
	if (list_empty(&tz->sensor.threshold_list))

		return 0;



	list_for_each_entry_safe(pos, var, &tz->sensor.threshold_list, list) {

	rcu_read_lock();

	list_for_each_entry_rcu(pos, &tz->sensor.threshold_list, list) {

		if ((pos->trip != trip) || (!pos->active))

			continue;

		if (((trip == THERMAL_TRIP_CONFIGURABLE_LOW) &&
@@ -415,6 +416,7 @@ int thermal_sensor_trip(struct thermal_zone_device *tz, 
			pos->notify(trip, temp, pos->data);

		}

	}

	rcu_read_unlock();



	schedule_work(&tz->sensor.work);
@@ -461,7 +463,7 @@ EXPORT_SYMBOL(sensor_activate_trip); 


int sensor_set_trip(uint32_t sensor_id, struct sensor_threshold *threshold)

{

	struct sensor_threshold *pos, *var;

	struct sensor_threshold *pos = NULL;

	struct sensor_info *sensor = get_sensor(sensor_id);



	if (!sensor)
@@ -471,14 +473,14 @@ int sensor_set_trip(uint32_t sensor_id, struct sensor_threshold *threshold) 
		return -EFAULT;



	mutex_lock(&sensor->lock);

	list_for_each_entry_safe(pos, var, &sensor->threshold_list, list) {

	list_for_each_entry(pos, &sensor->threshold_list, list) {

		if (pos == threshold)

			break;

	}



	if (pos != threshold) {

		INIT_LIST_HEAD(&threshold->list);

		list_add(&threshold->list, &sensor->threshold_list);

		list_add_rcu(&threshold->list, &sensor->threshold_list);

	}

	threshold->active = 0; /* Do not allow active threshold right away */
@@ -491,7 +493,7 @@ EXPORT_SYMBOL(sensor_set_trip); 


int sensor_cancel_trip(uint32_t sensor_id, struct sensor_threshold *threshold)

{

	struct sensor_threshold *pos, *var;

	struct sensor_threshold *pos = NULL, *var = NULL;

	struct sensor_info *sensor = get_sensor(sensor_id);

	int ret = 0;
@@ -502,7 +504,7 @@ int sensor_cancel_trip(uint32_t sensor_id, struct sensor_threshold *threshold) 
	list_for_each_entry_safe(pos, var, &sensor->threshold_list, list) {

		if (pos == threshold) {

			pos->active = 0;

			list_del(&pos->list);

			list_del_rcu(&pos->list);

			break;

		}

	}
@@ -571,7 +573,7 @@ int sensor_init(struct thermal_zone_device *tz) 
	sensor->min_idx = -1;

	mutex_init(&sensor->lock);

	INIT_LIST_HEAD(&sensor->sensor_list);

	INIT_LIST_HEAD(&sensor->threshold_list);

	INIT_LIST_HEAD_RCU(&sensor->threshold_list);

	INIT_LIST_HEAD(&tz->tz_threshold[0].list);

	INIT_LIST_HEAD(&tz->tz_threshold[1].list);

	tz->tz_threshold[0].notify = tz_notify_trip;