Re: [PATCH] leds: avoid races with workqueue

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

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Hi!

> >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);
> 
> Is this really required here? It creates non-uniform brightness
> setting behavior depending on whether it is set from sysfs or
> by in-kernel call to led_set_brightness().

This fixes the echo 0 > brightness; echo 1 > brightness. It has to be
at a place where we can sleep.

If you have better idea, it is welcome, but it would be good to fix
the bug.

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

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