linux-kernel - [PATCH] leds: triggers: flush pending brightness before activating trigger

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Message-Id: <20240603-led-trigger-flush-v1-1-c904c6e2fb34@weissschuh.net>
Date: Mon, 03 Jun 2024 23:45:29 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Pavel Machek <pavel@....cz>, Lee Jones <lee@...nel.org>, 
 Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc: linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Dustin Howett <dustin@...ett.net>, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH] leds: triggers: flush pending brightness before activating
 trigger

The race fixed in timer_trig_activate() between a blocking
set_brightness() call and trigger->activate() can affect any trigger.
So move the call to flush_work() into led_trigger_set() where it can
avoid the race for all triggers.

Fixes: 0db37915d912 ("leds: avoid races with workqueue")
Fixes: 8c0f693c6eff ("leds: avoid flush_work in atomic context")
Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
Dustin, could you validate that this fixes the issue you encountered in
the cros_ec led driver?
---
 drivers/leds/led-triggers.c          | 10 ++++++++--
 drivers/leds/trigger/ledtrig-timer.c |  5 -----
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index b1b323b19301..9e6233dbcfd4 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -195,10 +195,16 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 		led_cdev->trigger = trig;
 
 		ret = 0;
-		if (trig->activate)
+		if (trig->activate) {
+			/*
+			 * If "set brightness to 0" is pending in workqueue,
+			 * we don't want that to be reordered after ->activate()
+			 */
+			flush_work(&led_cdev->set_brightness_work);
 			ret = trig->activate(led_cdev);
-		else
+		} else {
 			led_set_brightness(led_cdev, trig->brightness);
+		}
 		if (ret)
 			goto err_activate;
 
diff --git a/drivers/leds/trigger/ledtrig-timer.c b/drivers/leds/trigger/ledtrig-timer.c
index b4688d1d9d2b..1d213c999d40 100644
--- a/drivers/leds/trigger/ledtrig-timer.c
+++ b/drivers/leds/trigger/ledtrig-timer.c
@@ -110,11 +110,6 @@ static int timer_trig_activate(struct led_classdev *led_cdev)
 		led_cdev->flags &= ~LED_INIT_DEFAULT_TRIGGER;
 	}
 
-	/*
-	 * 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);
 	led_blink_set(led_cdev, &led_cdev->blink_delay_on,
 		      &led_cdev->blink_delay_off);
 

---
base-commit: f06ce441457d4abc4d76be7acba26868a2d02b1c
change-id: 20240603-led-trigger-flush-3bef303eb902

Best regards,
-- 
Thomas Weißschuh <linux@...ssschuh.net>