linux-kernel - [RFC PATCH for 6.13 v1 08/20] thermal: core: Consolidate thermal zone locking in the exit path

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Message-ID: <7729094.EvYhyI6sBW@rjwysocki.net>
Date: Sat, 14 Sep 2024 12:35:20 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>,
 Lukasz Luba <lukasz.luba@....com>, Zhang Rui <rui.zhang@...el.com>
Subject:
 [RFC PATCH for 6.13 v1 08/20] thermal: core: Consolidate thermal zone locking
 in the exit path

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

In analogy with a previous change in the thermal zone initialization
path, to avoid acquiring the thermal zone lock and releasing it multiple
times back-to-back unnecessarily, move all of the code running under
thermal_list_lock in thermal_zone_device_unregister() into
thermal_zone_exit() and make the latter acquire the thermal zone lock
only once and release it along with thermal_list_lock.

For this purpose, provide an "unlocked" variant of
thermal_zone_cdev_unbind() to be called by thermal_zone_exit()
under the thermal zone lock.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/thermal/thermal_core.c |   53 +++++++++++++++++++++++------------------
 1 file changed, 30 insertions(+), 23 deletions(-)

Index: linux-pm/drivers/thermal/thermal_core.c
===================================================================
--- linux-pm.orig/drivers/thermal/thermal_core.c
+++ linux-pm/drivers/thermal/thermal_core.c
@@ -1249,17 +1249,23 @@ unlock_list:
 }
 EXPORT_SYMBOL_GPL(thermal_cooling_device_update);
 
-static void thermal_zone_cdev_unbind(struct thermal_zone_device *tz,
+static void __thermal_zone_cdev_unbind(struct thermal_zone_device *tz,
 				     struct thermal_cooling_device *cdev)
 {
 	struct thermal_trip_desc *td;
 
-	guard(thermal_zone)(tz);
-
 	for_each_trip_desc(tz, td)
 		thermal_unbind_cdev_from_trip(tz, td, cdev);
 }
 
+static void thermal_zone_cdev_unbind(struct thermal_zone_device *tz,
+				     struct thermal_cooling_device *cdev)
+{
+	guard(thermal_zone)(tz);
+
+	__thermal_zone_cdev_unbind(tz, cdev);
+}
+
 /**
  * thermal_cooling_device_unregister - removes a thermal cooling device
  * @cdev:	the thermal cooling device to remove.
@@ -1563,12 +1569,31 @@ struct device *thermal_zone_device(struc
 }
 EXPORT_SYMBOL_GPL(thermal_zone_device);
 
-static void thermal_zone_exit(struct thermal_zone_device *tz)
+static bool thermal_zone_exit(struct thermal_zone_device *tz)
 {
+	struct thermal_cooling_device *cdev;
+	bool ret = true;
+
+	mutex_lock(&thermal_list_lock);
+
+	if (list_empty(&tz->node)) {
+		ret = false;
+		goto unlock;
+	}
+
 	guard(thermal_zone)(tz);
 
 	tz->state |= TZ_STATE_FLAG_EXIT;
 	list_del(&tz->node);
+
+	/* Unbind all cdevs associated with this thermal zone. */
+	list_for_each_entry(cdev, &thermal_cdev_list, node)
+		__thermal_zone_cdev_unbind(tz, cdev);
+
+unlock:
+	mutex_unlock(&thermal_list_lock);
+
+	return ret;
 }
 
 /**
@@ -1577,31 +1602,13 @@ static void thermal_zone_exit(struct the
  */
 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
 {
-	struct thermal_cooling_device *cdev;
-	struct thermal_zone_device *pos = NULL;
-
 	if (!tz)
 		return;
 
 	thermal_debug_tz_remove(tz);
 
-	mutex_lock(&thermal_list_lock);
-	list_for_each_entry(pos, &thermal_tz_list, node)
-		if (pos == tz)
-			break;
-	if (pos != tz) {
-		/* thermal zone device not found */
-		mutex_unlock(&thermal_list_lock);
+	if (!thermal_zone_exit(tz))
 		return;
-	}
-
-	thermal_zone_exit(tz);
-
-	/* Unbind all cdevs associated with 'this' thermal zone */
-	list_for_each_entry(cdev, &thermal_cdev_list, node)
-		thermal_zone_cdev_unbind(tz, cdev);
-
-	mutex_unlock(&thermal_list_lock);
 
 	cancel_delayed_work_sync(&tz->poll_queue);