[PATCH AUTOSEL 6.7 18/18] thermal: core: Fix thermal zone suspend-resume synchronization

Sasha Levin
2024-01-16T00:13:40Z

From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>

[ Upstream commit 4e814173a8c4f432fd068b1c796f0416328c9d99 ]

There are 3 synchronization issues with thermal zone suspend-resume
during system-wide transitions:

1. The resume code runs in a PM notifier which is invoked after user
space has been thawed, so it can run concurrently with user space
which can trigger a thermal zone device removal. If that happens,
the thermal zone resume code may use a stale pointer to the next
list element and crash, because it does not hold thermal_list_lock
while walking thermal_tz_list.

2. The thermal zone resume code calls thermal_zone_device_init()
outside the zone lock, so user space or an update triggered by
the platform firmware may see an inconsistent state of a
thermal zone leading to unexpected behavior.

3. Clearing the in_suspend global variable in thermal_pm_notify()
allows __thermal_zone_device_update() to continue for all thermal
zones and it may as well run before the thermal_tz_list walk (or
at any point during the list walk for that matter) and attempt to
operate on a thermal zone that has not been resumed yet. It may
also race destructively with thermal_zone_device_init().

To address these issues, add thermal_list_lock locking to
thermal_pm_notify(), especially arount the thermal_tz_list,
make it call thermal_zone_device_init() back-to-back with
__thermal_zone_device_update() under the zone lock and replace
in_suspend with per-zone bool "suspend" indicators set and unset
under the given zone's lock.

Link: https://lore.kernel.org/linux-pm/20231218162348.69101-1-bo.ye@mediatek.com/
Reported-by: Bo Ye <bo.ye@mediatek.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/thermal/thermal_core.c | 30 +++++++++++++++++++++++-------
include/linux/thermal.h | 2 ++
2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
index 9c17d35ccbbd..fe3bcfba4d67 100644
--- a/drivers/thermal/thermal_core.c
+++ b/drivers/thermal/thermal_core.c
@@ -37,8 +37,6 @@ static LIST_HEAD(thermal_governor_list);
static DEFINE_MUTEX(thermal_list_lock);
static DEFINE_MUTEX(thermal_governor_lock);

-static atomic_t in_suspend;
-
static struct thermal_governor *def_governor;

/*
@@ -405,7 +403,7 @@ void __thermal_zone_device_update(struct thermal_zone_device *tz,
{
const struct thermal_trip *trip;

- if (atomic_read(&in_suspend))
+ if (tz->suspended)
return;

if (WARN_ONCE(!tz->ops->get_temp,
@@ -1515,17 +1513,35 @@ static int thermal_pm_notify(struct notifier_block *nb,
case PM_HIBERNATION_PREPARE:
case PM_RESTORE_PREPARE:
case PM_SUSPEND_PREPARE:
- atomic_set(&in_suspend, 1);
+ mutex_lock(&thermal_list_lock);
+
+ list_for_each_entry(tz, &thermal_tz_list, node) {
+ mutex_lock(&tz->lock);
+
+ tz->suspended = true;
+
+ mutex_unlock(&tz->lock);
+ }
+
+ mutex_unlock(&thermal_list_lock);
break;
case PM_POST_HIBERNATION:
case PM_POST_RESTORE:
case PM_POST_SUSPEND:
- atomic_set(&in_suspend, 0);
+ mutex_lock(&thermal_list_lock);
+
list_for_each_entry(tz, &thermal_tz_list, node) {
+ mutex_lock(&tz->lock);
+
+ tz->suspended = false;
+
thermal_zone_device_init(tz);
- thermal_zone_device_update(tz,
- THERMAL_EVENT_UNSPECIFIED);
+ __thermal_zone_device_update(tz, THERMAL_EVENT_UNSPECIFIED);
+
+ mutex_unlock(&tz->lock);
}
+
+ mutex_unlock(&thermal_list_lock);
break;
default:
break;
diff --git a/include/linux/thermal.h b/include/linux/thermal.h
index cee814d5d1ac..1da1739d75d9 100644
--- a/include/linux/thermal.h
+++ b/include/linux/thermal.h
@@ -149,6 +149,7 @@ struct thermal_cooling_device {
* @node: node in thermal_tz_list (in thermal_core.c)
* @poll_queue: delayed work for polling
* @notify_event: Last notification event
+ * @suspended: thermal zone suspend indicator
*/
struct thermal_zone_device {
int id;
@@ -181,6 +182,7 @@ struct thermal_zone_device {
struct list_head node;
struct delayed_work poll_queue;
enum thermal_notify_event notify_event;
+ bool suspended;
};

/**
--
2.43.0