[PATCH] leds: avoid races with workqueue

[Pavel Machek <pavel-+ZI9xUNit7I@public.gmane.org>]

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There are races between "main" thread and workqueue. They manifest
themselves on Thinkpad X60:
    
This should result in LED blinking, but it turns it off instead:
    
    root@amd:/data/pavel# cd /sys/class/leds/tpacpi\:\:power
    root@amd:/sys/class/leds/tpacpi::power# echo timer > trigger
    root@amd:/sys/class/leds/tpacpi::power# echo timer > trigger
    root@amd:/sys/class/leds/tpacpi::power#
    
It should be possible to transition from blinking to solid on by echo
0 > brightness; echo 1 > brightness... but that does not work, either,
if done too quickly.
    
Synchronization of the workqueue fixes both.
    
Signed-off-by: Pavel Machek <pavel-+ZI9xUNit7I@public.gmane.org>

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 68aa923..dcb59c8 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -57,6 +57,7 @@ static ssize_t brightness_store(struct device *dev,
 	if (state == LED_OFF)
 		led_trigger_remove(led_cdev);
 	led_set_brightness(led_cdev, state);
+	flush_work(&led_cdev->set_brightness_work);
 
 	ret = size;
 unlock:
diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
index 9f8da39..aefac4d 100644
--- a/drivers/leds/led-core.c
+++ b/drivers/leds/led-core.c
@@ -166,6 +166,11 @@ static void led_blink_setup(struct led_classdev *led_cdev,
 		     unsigned long *delay_on,
 		     unsigned long *delay_off)
 {
+	/*
+	 * 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);
 	if (!test_bit(LED_BLINK_ONESHOT, &led_cdev->work_flags) &&
 	    led_cdev->blink_set &&
 	    !led_cdev->blink_set(led_cdev, delay_on, delay_off))

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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