leds: avoid races with workqueue

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

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.

Fixes: 1afcadfcd184 ("leds: core: Use set_brightness_work for the blocking op")
Signed-off-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 3c7e348..85848c5 100644 (file)
--- 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 e3da7c0..e9ae7f8 100644 (file)
--- a/drivers/leds/led-core.c
+++ b/drivers/leds/led-core.c
@@ -164,6 +164,11 @@ 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))