Re: [PATCH] leds: avoid races with workqueue

[Jacek Anaszewski <jacek.anaszewski-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi Pavel,

On 5/1/19 8:36 PM, Pavel Machek wrote:
> 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#

I believe this line is redundant, so I removed it.

>>> 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.

Currently not, so I applied the patch in this shape.

-- 
Best regards,
Jacek Anaszewski