leds: triggers: Flush pending brightness before activating trigger

The race fixed in timer_trig_activate() between a blocking
set_brightness() call and trigger->activate() can affect any trigger.
So move the call to flush_work() into led_trigger_set() where it can
avoid the race for all triggers.

Fixes: 0db37915 ("leds: avoid races with workqueue")
Fixes: 8c0f693c ("leds: avoid flush_work in atomic context")
Cc: stable@vger.kernel.org
Tested-by: Dustin L. Howett <dustin@howett.net>
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20240613-led-trigger-flush-v2-1-f4f970799d77@weissschuh.netSigned-off-by: Lee Jones <lee@kernel.org>

drivers/leds/led-triggers.c

@@ -201,6 +201,12 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 		 */
 		synchronize_rcu();
 
+		/*
+		 * If "set brightness to 0" is pending in workqueue,
+		 * we don't want that to be reordered after ->activate()
+		 */
+		flush_work(&led_cdev->set_brightness_work);
+
 		ret = 0;
 		if (trig->activate)
 			ret = trig->activate(led_cdev);

drivers/leds/trigger/ledtrig-timer.c

@@ -110,11 +110,6 @@ static int timer_trig_activate(struct led_classdev *led_cdev)
 		led_cdev->flags &= ~LED_INIT_DEFAULT_TRIGGER;
 	}
 
-	/*
-	 * If "set brightness to 0" is pending in workqueue, we don't
-	 * want that to be reordered after blink_set()
-	 */
-	flush_work(&led_cdev->set_brightness_work);
 	led_blink_set(led_cdev, &led_cdev->blink_delay_on,
 		      &led_cdev->blink_delay_off);