[RESEND,2/4] leds: Fix set_brightness_delayed() race

Commit Message

Hans de Goede May 10, 2023, 4:22 p.m. UTC

When a trigger wants to switch from blinking to LED on it needs to call:
	led_set_brightness(LED_OFF);
	led_set_brightness(LED_FULL);

To first call disables blinking and the second then turns the LED on
(the power-supply charging-blink-full-solid triggers do this).

These calls happen immediately after each other, so it is possible
that set_brightness_delayed() from the first call has not run yet
when the led_set_brightness(LED_FULL) call finishes.

If this race hits then this is causing problems for both
sw- and hw-blinking:

For sw-blinking set_brightness_delayed() clears delayed_set_value
when LED_BLINK_DISABLE is set causing the led_set_brightness(LED_FULL)
call effects to get lost when hitting the race, resulting in the LED
turning off instead of on.

For hw-blinking if the race hits delayed_set_value has been
set to LED_FULL by the time set_brightness_delayed() runs.
So led_cdev->brightness_set_blocking() is never called with
LED_OFF as argument and the hw-blinking is never disabled leaving
the LED blinking instead of on.

Fix both issues by adding LED_SET_BRIGHTNESS and LED_SET_BRIGHTNESS_OFF
work_flags making this 2 separate actions to be run by
set_brightness_delayed().

Reviewed-by: Jacek Anaszewski <[e-mail]>
Tested-by: Yauhen Kharuzhy <[e-mail]>
Signed-off-by: Hans de Goede <[e-mail]>
---
 drivers/leds/led-core.c | 57 +++++++++++++++++++++++++++++++----------
 include/linux/leds.h    |  3 +++
 2 files changed, 47 insertions(+), 13 deletions(-)

Comments

Lee Jones May 18, 2023, 12:13 p.m. UTC | #1

On Wed, 10 May 2023, Hans de Goede wrote:

> When a trigger wants to switch from blinking to LED on it needs to call:
> 	led_set_brightness(LED_OFF);
> 	led_set_brightness(LED_FULL);
> 
> To first call disables blinking and the second then turns the LED on
> (the power-supply charging-blink-full-solid triggers do this).
> 
> These calls happen immediately after each other, so it is possible
> that set_brightness_delayed() from the first call has not run yet
> when the led_set_brightness(LED_FULL) call finishes.
> 
> If this race hits then this is causing problems for both
> sw- and hw-blinking:
> 
> For sw-blinking set_brightness_delayed() clears delayed_set_value
> when LED_BLINK_DISABLE is set causing the led_set_brightness(LED_FULL)
> call effects to get lost when hitting the race, resulting in the LED
> turning off instead of on.
> 
> For hw-blinking if the race hits delayed_set_value has been
> set to LED_FULL by the time set_brightness_delayed() runs.
> So led_cdev->brightness_set_blocking() is never called with
> LED_OFF as argument and the hw-blinking is never disabled leaving
> the LED blinking instead of on.
> 
> Fix both issues by adding LED_SET_BRIGHTNESS and LED_SET_BRIGHTNESS_OFF
> work_flags making this 2 separate actions to be run by
> set_brightness_delayed().
> 
> Reviewed-by: Jacek Anaszewski <[e-mail]>
> Tested-by: Yauhen Kharuzhy <[e-mail]>
> Signed-off-by: Hans de Goede <[e-mail]>
> ---
>  drivers/leds/led-core.c | 57 +++++++++++++++++++++++++++++++----------
>  include/linux/leds.h    |  3 +++
>  2 files changed, 47 insertions(+), 13 deletions(-)

Applied, thanks

Patch

diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
index 4a97cb745788..e61acc785410 100644
--- a/drivers/leds/led-core.c
+++ b/drivers/leds/led-core.c
@@ -114,21 +114,14 @@  static void led_timer_function(struct timer_list *t)
 	mod_timer(&led_cdev->blink_timer, jiffies + msecs_to_jiffies(delay));
 }
 
-static void set_brightness_delayed(struct work_struct *ws)
+static void set_brightness_delayed_set_brightness(struct led_classdev *led_cdev,
+						  unsigned int value)
 {
-	struct led_classdev *led_cdev =
-		container_of(ws, struct led_classdev, set_brightness_work);
 	int ret = 0;
 
-	if (test_and_clear_bit(LED_BLINK_DISABLE, &led_cdev->work_flags)) {
-		led_cdev->delayed_set_value = LED_OFF;
-		led_stop_software_blink(led_cdev);
-	}
-
-	ret = __led_set_brightness(led_cdev, led_cdev->delayed_set_value);
+	ret = __led_set_brightness(led_cdev, value);
 	if (ret == -ENOTSUPP)
-		ret = __led_set_brightness_blocking(led_cdev,
-					led_cdev->delayed_set_value);
+		ret = __led_set_brightness_blocking(led_cdev, value);
 	if (ret < 0 &&
 	    /* LED HW might have been unplugged, therefore don't warn */
 	    !(ret == -ENODEV && (led_cdev->flags & LED_UNREGISTERING) &&
@@ -137,6 +130,30 @@  static void set_brightness_delayed(struct work_struct *ws)
 			"Setting an LED's brightness failed (%d)\n", ret);
 }
 
+static void set_brightness_delayed(struct work_struct *ws)
+{
+	struct led_classdev *led_cdev =
+		container_of(ws, struct led_classdev, set_brightness_work);
+
+	if (test_and_clear_bit(LED_BLINK_DISABLE, &led_cdev->work_flags)) {
+		led_stop_software_blink(led_cdev);
+		set_bit(LED_SET_BRIGHTNESS_OFF, &led_cdev->work_flags);
+	}
+
+	/*
+	 * Triggers may call led_set_brightness(LED_OFF),
+	 * led_set_brightness(LED_FULL) in quick succession to disable blinking
+	 * and turn the LED on. Both actions may have been scheduled to run
+	 * before this work item runs once. To make sure this works properly
+	 * handle LED_SET_BRIGHTNESS_OFF first.
+	 */
+	if (test_and_clear_bit(LED_SET_BRIGHTNESS_OFF, &led_cdev->work_flags))
+		set_brightness_delayed_set_brightness(led_cdev, LED_OFF);
+
+	if (test_and_clear_bit(LED_SET_BRIGHTNESS, &led_cdev->work_flags))
+		set_brightness_delayed_set_brightness(led_cdev, led_cdev->delayed_set_value);
+}
+
 static void led_set_software_blink(struct led_classdev *led_cdev,
 				   unsigned long delay_on,
 				   unsigned long delay_off)
@@ -271,8 +288,22 @@  void led_set_brightness_nopm(struct led_classdev *led_cdev, unsigned int value)
 	if (!__led_set_brightness(led_cdev, value))
 		return;
 
-	/* If brightness setting can sleep, delegate it to a work queue task */
-	led_cdev->delayed_set_value = value;
+	/*
+	 * Brightness setting can sleep, delegate it to a work queue task.
+	 * value 0 / LED_OFF is special, since it also disables hw-blinking
+	 * (sw-blink disable is handled in led_set_brightness()).
+	 * To avoid a hw-blink-disable getting lost when a second brightness
+	 * change is done immediately afterwards (before the work runs),
+	 * it uses a separate work_flag.
+	 */
+	if (value) {
+		led_cdev->delayed_set_value = value;
+		set_bit(LED_SET_BRIGHTNESS, &led_cdev->work_flags);
+	} else {
+		clear_bit(LED_SET_BRIGHTNESS, &led_cdev->work_flags);
+		set_bit(LED_SET_BRIGHTNESS_OFF, &led_cdev->work_flags);
+	}
+
 	schedule_work(&led_cdev->set_brightness_work);
 }
 EXPORT_SYMBOL_GPL(led_set_brightness_nopm);
diff --git a/include/linux/leds.h b/include/linux/leds.h
index c3dc22d184e2..de813fe96a20 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -124,6 +124,9 @@  struct led_classdev {
 #define LED_BLINK_INVERT		3
 #define LED_BLINK_BRIGHTNESS_CHANGE 	4
 #define LED_BLINK_DISABLE		5
+	/* Brightness off also disables hw-blinking so it is a separate action */
+#define LED_SET_BRIGHTNESS_OFF		6
+#define LED_SET_BRIGHTNESS		7
 
 	/* Set LED brightness level
 	 * Must not sleep. Use brightness_set_blocking for drivers