linux/drivers/thermal/step_wise.c
Michele Di Giorgio d0b7306d20 thermal: fix race condition when updating cooling device
When multiple thermal zones are bound to the same cooling device, multiple
kernel threads may want to update the cooling device state by calling
thermal_cdev_update(). Having cdev not protected by a mutex can lead to a race
condition. Consider the following situation with two kernel threads k1 and k2:

	    Thread k1				Thread k2
                                    ||
                                    ||  call thermal_cdev_update()
                                    ||      ...
                                    ||      set_cur_state(cdev, target);
    call power_actor_set_power()    ||
        ...                         ||
        instance->target = state;   ||
        cdev->updated = false;      ||
                                    ||      cdev->updated = true;
                                    ||      // completes execution
    call thermal_cdev_update()      ||
        // cdev->updated == true    ||
        return;                     ||
                                    \/
                                    time

k2 has already looped through the thermal instances looking for the deepest
cooling device state and is preempted right before setting cdev->updated to
true. Now, k1 runs, modifies the thermal instance state and sets cdev->updated
to false. Then, k1 is preempted and k2 continues the execution by setting
cdev->updated to true, therefore preventing k1 from performing the update.
Notice that this is not an issue if k2 looks at the instance->target modified by
k1 "after" it is assigned by k1. In fact, in this case the update will happen
anyway and k1 can safely return immediately from thermal_cdev_update().

This may lead to a situation where a thermal governor never updates the cooling
device. For example, this is the case for the step_wise governor: when calling
the function thermal_zone_trip_update(), the governor may always get a new state
equal to the old one (which, however, wasn't notified to the cooling device) and
will therefore skip the update.

CC: Zhang Rui <rui.zhang@intel.com>
CC: Eduardo Valentin <edubezval@gmail.com>
CC: Peter Feuerer <peter@piie.net>
Reported-by: Toby Huang <toby.huang@arm.com>
Signed-off-by: Michele Di Giorgio <michele.digiorgio@arm.com>
Reviewed-by: Javi Merino <javi.merino@arm.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
2016-08-08 10:57:39 +08:00

231 lines
6.7 KiB
C

/*
* step_wise.c - A step-by-step Thermal throttling governor
*
* Copyright (C) 2012 Intel Corp
* Copyright (C) 2012 Durgadoss R <durgadoss.r@intel.com>
*
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2 of the License.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
*
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
#include <linux/thermal.h>
#include <trace/events/thermal.h>
#include "thermal_core.h"
/*
* If the temperature is higher than a trip point,
* a. if the trend is THERMAL_TREND_RAISING, use higher cooling
* state for this trip point
* b. if the trend is THERMAL_TREND_DROPPING, use lower cooling
* state for this trip point
* c. if the trend is THERMAL_TREND_RAISE_FULL, use upper limit
* for this trip point
* d. if the trend is THERMAL_TREND_DROP_FULL, use lower limit
* for this trip point
* If the temperature is lower than a trip point,
* a. if the trend is THERMAL_TREND_RAISING, do nothing
* b. if the trend is THERMAL_TREND_DROPPING, use lower cooling
* state for this trip point, if the cooling state already
* equals lower limit, deactivate the thermal instance
* c. if the trend is THERMAL_TREND_RAISE_FULL, do nothing
* d. if the trend is THERMAL_TREND_DROP_FULL, use lower limit,
* if the cooling state already equals lower limit,
* deactivate the thermal instance
*/
static unsigned long get_target_state(struct thermal_instance *instance,
enum thermal_trend trend, bool throttle)
{
struct thermal_cooling_device *cdev = instance->cdev;
unsigned long cur_state;
unsigned long next_target;
/*
* We keep this instance the way it is by default.
* Otherwise, we use the current state of the
* cdev in use to determine the next_target.
*/
cdev->ops->get_cur_state(cdev, &cur_state);
next_target = instance->target;
dev_dbg(&cdev->device, "cur_state=%ld\n", cur_state);
if (!instance->initialized) {
if (throttle) {
next_target = (cur_state + 1) >= instance->upper ?
instance->upper :
((cur_state + 1) < instance->lower ?
instance->lower : (cur_state + 1));
} else {
next_target = THERMAL_NO_TARGET;
}
return next_target;
}
switch (trend) {
case THERMAL_TREND_RAISING:
if (throttle) {
next_target = cur_state < instance->upper ?
(cur_state + 1) : instance->upper;
if (next_target < instance->lower)
next_target = instance->lower;
}
break;
case THERMAL_TREND_RAISE_FULL:
if (throttle)
next_target = instance->upper;
break;
case THERMAL_TREND_DROPPING:
if (cur_state <= instance->lower) {
if (!throttle)
next_target = THERMAL_NO_TARGET;
} else {
next_target = cur_state - 1;
if (next_target > instance->upper)
next_target = instance->upper;
}
break;
case THERMAL_TREND_DROP_FULL:
if (cur_state == instance->lower) {
if (!throttle)
next_target = THERMAL_NO_TARGET;
} else
next_target = instance->lower;
break;
default:
break;
}
return next_target;
}
static void update_passive_instance(struct thermal_zone_device *tz,
enum thermal_trip_type type, int value)
{
/*
* If value is +1, activate a passive instance.
* If value is -1, deactivate a passive instance.
*/
if (type == THERMAL_TRIP_PASSIVE || type == THERMAL_TRIPS_NONE)
tz->passive += value;
}
static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
{
int trip_temp;
enum thermal_trip_type trip_type;
enum thermal_trend trend;
struct thermal_instance *instance;
bool throttle = false;
int old_target;
if (trip == THERMAL_TRIPS_NONE) {
trip_temp = tz->forced_passive;
trip_type = THERMAL_TRIPS_NONE;
} else {
tz->ops->get_trip_temp(tz, trip, &trip_temp);
tz->ops->get_trip_type(tz, trip, &trip_type);
}
trend = get_tz_trend(tz, trip);
if (tz->temperature >= trip_temp) {
throttle = true;
trace_thermal_zone_trip(tz, trip, trip_type);
}
dev_dbg(&tz->device, "Trip%d[type=%d,temp=%d]:trend=%d,throttle=%d\n",
trip, trip_type, trip_temp, trend, throttle);
mutex_lock(&tz->lock);
list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
if (instance->trip != trip)
continue;
old_target = instance->target;
instance->target = get_target_state(instance, trend, throttle);
dev_dbg(&instance->cdev->device, "old_target=%d, target=%d\n",
old_target, (int)instance->target);
if (instance->initialized && old_target == instance->target)
continue;
/* Activate a passive thermal instance */
if (old_target == THERMAL_NO_TARGET &&
instance->target != THERMAL_NO_TARGET)
update_passive_instance(tz, trip_type, 1);
/* Deactivate a passive thermal instance */
else if (old_target != THERMAL_NO_TARGET &&
instance->target == THERMAL_NO_TARGET)
update_passive_instance(tz, trip_type, -1);
instance->initialized = true;
mutex_lock(&instance->cdev->lock);
instance->cdev->updated = false; /* cdev needs update */
mutex_unlock(&instance->cdev->lock);
}
mutex_unlock(&tz->lock);
}
/**
* step_wise_throttle - throttles devices associated with the given zone
* @tz - thermal_zone_device
* @trip - the trip point
* @trip_type - type of the trip point
*
* Throttling Logic: This uses the trend of the thermal zone to throttle.
* If the thermal zone is 'heating up' this throttles all the cooling
* devices associated with the zone and its particular trip point, by one
* step. If the zone is 'cooling down' it brings back the performance of
* the devices by one step.
*/
static int step_wise_throttle(struct thermal_zone_device *tz, int trip)
{
struct thermal_instance *instance;
thermal_zone_trip_update(tz, trip);
if (tz->forced_passive)
thermal_zone_trip_update(tz, THERMAL_TRIPS_NONE);
mutex_lock(&tz->lock);
list_for_each_entry(instance, &tz->thermal_instances, tz_node)
thermal_cdev_update(instance->cdev);
mutex_unlock(&tz->lock);
return 0;
}
static struct thermal_governor thermal_gov_step_wise = {
.name = "step_wise",
.throttle = step_wise_throttle,
};
int thermal_gov_step_wise_register(void)
{
return thermal_register_governor(&thermal_gov_step_wise);
}
void thermal_gov_step_wise_unregister(void)
{
thermal_unregister_governor(&thermal_gov_step_wise);
}