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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>
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|---|---|---|
| .. | ||
| int340x_thermal | ||
| samsung | ||
| st | ||
| tegra | ||
| ti-soc-thermal | ||
| armada_thermal.c | ||
| clock_cooling.c | ||
| cpu_cooling.c | ||
| db8500_cpufreq_cooling.c | ||
| db8500_thermal.c | ||
| devfreq_cooling.c | ||
| dove_thermal.c | ||
| fair_share.c | ||
| gov_bang_bang.c | ||
| hisi_thermal.c | ||
| imx_thermal.c | ||
| intel_pch_thermal.c | ||
| intel_powerclamp.c | ||
| intel_quark_dts_thermal.c | ||
| intel_soc_dts_iosf.c | ||
| intel_soc_dts_iosf.h | ||
| intel_soc_dts_thermal.c | ||
| Kconfig | ||
| kirkwood_thermal.c | ||
| Makefile | ||
| mtk_thermal.c | ||
| of-thermal.c | ||
| power_allocator.c | ||
| qcom-spmi-temp-alarm.c | ||
| rcar_thermal.c | ||
| rockchip_thermal.c | ||
| spear_thermal.c | ||
| step_wise.c | ||
| tango_thermal.c | ||
| thermal_core.c | ||
| thermal_core.h | ||
| thermal_hwmon.c | ||
| thermal_hwmon.h | ||
| thermal-generic-adc.c | ||
| user_space.c | ||
| x86_pkg_temp_thermal.c | ||