mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-15 08:46:45 +07:00
d0b7306d20
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>
139 lines
3.9 KiB
C
139 lines
3.9 KiB
C
/*
|
|
* gov_bang_bang.c - A simple thermal throttling governor using hysteresis
|
|
*
|
|
* Copyright (C) 2014 Peter Feuerer <peter@piie.net>
|
|
*
|
|
* Based on step_wise.c with following Copyrights:
|
|
* 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.
|
|
*
|
|
* 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.
|
|
*
|
|
*/
|
|
|
|
#include <linux/thermal.h>
|
|
|
|
#include "thermal_core.h"
|
|
|
|
static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
|
|
{
|
|
int trip_temp, trip_hyst;
|
|
struct thermal_instance *instance;
|
|
|
|
tz->ops->get_trip_temp(tz, trip, &trip_temp);
|
|
|
|
if (!tz->ops->get_trip_hyst) {
|
|
pr_warn_once("Undefined get_trip_hyst for thermal zone %s - "
|
|
"running with default hysteresis zero\n", tz->type);
|
|
trip_hyst = 0;
|
|
} else
|
|
tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
|
|
|
|
dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
|
|
trip, trip_temp, tz->temperature,
|
|
trip_hyst);
|
|
|
|
mutex_lock(&tz->lock);
|
|
|
|
list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
|
|
if (instance->trip != trip)
|
|
continue;
|
|
|
|
/* in case fan is in initial state, switch the fan off */
|
|
if (instance->target == THERMAL_NO_TARGET)
|
|
instance->target = 0;
|
|
|
|
/* in case fan is neither on nor off set the fan to active */
|
|
if (instance->target != 0 && instance->target != 1) {
|
|
pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
|
|
instance->name, instance->target);
|
|
instance->target = 1;
|
|
}
|
|
|
|
/*
|
|
* enable fan when temperature exceeds trip_temp and disable
|
|
* the fan in case it falls below trip_temp minus hysteresis
|
|
*/
|
|
if (instance->target == 0 && tz->temperature >= trip_temp)
|
|
instance->target = 1;
|
|
else if (instance->target == 1 &&
|
|
tz->temperature < trip_temp - trip_hyst)
|
|
instance->target = 0;
|
|
|
|
dev_dbg(&instance->cdev->device, "target=%d\n",
|
|
(int)instance->target);
|
|
|
|
mutex_lock(&instance->cdev->lock);
|
|
instance->cdev->updated = false; /* cdev needs update */
|
|
mutex_unlock(&instance->cdev->lock);
|
|
}
|
|
|
|
mutex_unlock(&tz->lock);
|
|
}
|
|
|
|
/**
|
|
* bang_bang_control - controls devices associated with the given zone
|
|
* @tz - thermal_zone_device
|
|
* @trip - the trip point
|
|
*
|
|
* Regulation Logic: a two point regulation, deliver cooling state depending
|
|
* on the previous state shown in this diagram:
|
|
*
|
|
* Fan: OFF ON
|
|
*
|
|
* |
|
|
* |
|
|
* trip_temp: +---->+
|
|
* | | ^
|
|
* | | |
|
|
* | | Temperature
|
|
* (trip_temp - hyst): +<----+
|
|
* |
|
|
* |
|
|
* |
|
|
*
|
|
* * If the fan is not running and temperature exceeds trip_temp, the fan
|
|
* gets turned on.
|
|
* * In case the fan is running, temperature must fall below
|
|
* (trip_temp - hyst) so that the fan gets turned off again.
|
|
*
|
|
*/
|
|
static int bang_bang_control(struct thermal_zone_device *tz, int trip)
|
|
{
|
|
struct thermal_instance *instance;
|
|
|
|
thermal_zone_trip_update(tz, trip);
|
|
|
|
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_bang_bang = {
|
|
.name = "bang_bang",
|
|
.throttle = bang_bang_control,
|
|
};
|
|
|
|
int thermal_gov_bang_bang_register(void)
|
|
{
|
|
return thermal_register_governor(&thermal_gov_bang_bang);
|
|
}
|
|
|
|
void thermal_gov_bang_bang_unregister(void)
|
|
{
|
|
thermal_unregister_governor(&thermal_gov_bang_bang);
|
|
}
|