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

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

[Sasha Levin]

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(+)

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 3c7e3487b373b..85848c5da705f 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 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))
-- 
2.20.1

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

[Pavel Machek]

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

[Sasha Levin]

On Sat, May 25, 2019 at 12:55:05AM +0200, Pavel Machek wrote:
>Hi!
>
>Could we hold this patch for now?

Sure, dropped. Thanks!

--
Thanks,
Sasha

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

[Pavel Machek]

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Hi!

> >Could we hold this patch for now?
> 
> Sure, dropped. Thanks!

So... fix for this now should be in mainline. But as original problem
is not too severe, I don't think we need to apply this or the fixed
version to stable.

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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