Merge tag 'leds-5.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/pavel/linux-leds

Pull LED updates from Pavel Machek:
 "Johannes pointed out that locking is still problematic with triggers
  list, attempt to solve that by using RCU"

* tag 'leds-5.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/pavel/linux-leds:
  leds: trigger: Disable CPU trigger on PREEMPT_RT
  leds: trigger: use RCU to protect the led_cdevs list
  led-class-flash: fix -Wrestrict warning

Author: torvalds

drivers/leds/led-class-flash.c

@@ -207,7 +207,7 @@ static ssize_t flash_fault_show(struct device *dev,
 		mask <<= 1;
 	}
 
-	return sprintf(buf, "%s\n", buf);
+	return strlen(strcat(buf, "\n"));
 }
 static DEVICE_ATTR_RO(flash_fault);
 

drivers/leds/led-triggers.c

@@ -157,7 +157,6 @@ EXPORT_SYMBOL_GPL(led_trigger_read);
 /* Caller must ensure led_cdev->trigger_lock held */
 int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 {
-	unsigned long flags;
 	char *event = NULL;
 	char *envp[2];
 	const char *name;
@@ -171,10 +170,13 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 
 	/* Remove any existing trigger */
 	if (led_cdev->trigger) {
-		write_lock_irqsave(&led_cdev->trigger->leddev_list_lock, flags);
-		list_del(&led_cdev->trig_list);
-		write_unlock_irqrestore(&led_cdev->trigger->leddev_list_lock,
-			flags);
+		spin_lock(&led_cdev->trigger->leddev_list_lock);
+		list_del_rcu(&led_cdev->trig_list);
+		spin_unlock(&led_cdev->trigger->leddev_list_lock);
+
+		/* ensure it's no longer visible on the led_cdevs list */
+		synchronize_rcu();
+
 		cancel_work_sync(&led_cdev->set_brightness_work);
 		led_stop_software_blink(led_cdev);
 		if (led_cdev->trigger->deactivate)
@@ -186,9 +188,9 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 		led_set_brightness(led_cdev, LED_OFF);
 	}
 	if (trig) {
-		write_lock_irqsave(&trig->leddev_list_lock, flags);
-		list_add_tail(&led_cdev->trig_list, &trig->led_cdevs);
-		write_unlock_irqrestore(&trig->leddev_list_lock, flags);
+		spin_lock(&trig->leddev_list_lock);
+		list_add_tail_rcu(&led_cdev->trig_list, &trig->led_cdevs);
+		spin_unlock(&trig->leddev_list_lock);
 		led_cdev->trigger = trig;
 
 		if (trig->activate)
@@ -223,9 +225,10 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 		trig->deactivate(led_cdev);
 err_activate:
 
-	write_lock_irqsave(&led_cdev->trigger->leddev_list_lock, flags);
-	list_del(&led_cdev->trig_list);
-	write_unlock_irqrestore(&led_cdev->trigger->leddev_list_lock, flags);
+	spin_lock(&led_cdev->trigger->leddev_list_lock);
+	list_del_rcu(&led_cdev->trig_list);
+	spin_unlock(&led_cdev->trigger->leddev_list_lock);
+	synchronize_rcu();
 	led_cdev->trigger = NULL;
 	led_cdev->trigger_data = NULL;
 	led_set_brightness(led_cdev, LED_OFF);
@@ -285,7 +288,7 @@ int led_trigger_register(struct led_trigger *trig)
 	struct led_classdev *led_cdev;
 	struct led_trigger *_trig;
 
-	rwlock_init(&trig->leddev_list_lock);
+	spin_lock_init(&trig->leddev_list_lock);
 	INIT_LIST_HEAD(&trig->led_cdevs);
 
 	down_write(&triggers_list_lock);
@@ -378,15 +381,14 @@ void led_trigger_event(struct led_trigger *trig,
 			enum led_brightness brightness)
 {
 	struct led_classdev *led_cdev;
-	unsigned long flags;
 
 	if (!trig)
 		return;
 
-	read_lock_irqsave(&trig->leddev_list_lock, flags);
-	list_for_each_entry(led_cdev, &trig->led_cdevs, trig_list)
+	rcu_read_lock();
+	list_for_each_entry_rcu(led_cdev, &trig->led_cdevs, trig_list)
 		led_set_brightness(led_cdev, brightness);
-	read_unlock_irqrestore(&trig->leddev_list_lock, flags);
+	rcu_read_unlock();
 }
 EXPORT_SYMBOL_GPL(led_trigger_event);
 
@@ -397,20 +399,19 @@ static void led_trigger_blink_setup(struct led_trigger *trig,
 			     int invert)
 {
 	struct led_classdev *led_cdev;
-	unsigned long flags;
 
 	if (!trig)
 		return;
 
-	read_lock_irqsave(&trig->leddev_list_lock, flags);
-	list_for_each_entry(led_cdev, &trig->led_cdevs, trig_list) {
+	rcu_read_lock();
+	list_for_each_entry_rcu(led_cdev, &trig->led_cdevs, trig_list) {
 		if (oneshot)
 			led_blink_set_oneshot(led_cdev, delay_on, delay_off,
 					      invert);
 		else
 			led_blink_set(led_cdev, delay_on, delay_off);
 	}
-	read_unlock_irqrestore(&trig->leddev_list_lock, flags);
+	rcu_read_unlock();
 }
 
 void led_trigger_blink(struct led_trigger *trig,

drivers/leds/trigger/Kconfig

@@ -64,6 +64,7 @@ config LEDS_TRIGGER_BACKLIGHT
 
 config LEDS_TRIGGER_CPU
 	bool "LED CPU Trigger"
+	depends on !PREEMPT_RT
 	help
 	  This allows LEDs to be controlled by active CPUs. This shows
 	  the active CPUs across an array of LEDs so you can see which

include/linux/leds.h

@@ -360,7 +360,7 @@ struct led_trigger {
 	struct led_hw_trigger_type *trigger_type;
 
 	/* LEDs under control by this trigger (for simple triggers) */
-	rwlock_t	  leddev_list_lock;
+	spinlock_t	  leddev_list_lock;
 	struct list_head  led_cdevs;
 
 	/* Link to next registered trigger */