Re: [PATCH AUTOSEL 5.1 033/375] leds: avoid races with workqueue

Pavel Machek
2019-05-24T22:55:11Z

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Hi!

Could we hold this patch for now?

> From: Pavel Machek <pavel@ucw.cz>
>
> [ Upstream commit 0db37915d912e8dc6588f25da76d3ed36718d92f ]
>
> 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>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> drivers/leds/led-class.c | 1 +
> drivers/leds/led-core.c | 5 +++++
> 2 files changed, 6 insertions(+)

> index e3da7c03da1b5..e9ae7f87ab900 100644
> --- 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))

This part is likely buggy. It seems triggers are using this from
atomic context... ledtrig-disk for example.

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

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