linux-kernel - [PATCH v2] LEDS: fix race between LED device uevent and actual attributes creation

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Message-Id: <201003101832.18867.ffainelli@freebox.fr>
Date:	Wed, 10 Mar 2010 18:32:18 +0100
From:	Florian Fainelli <ffainelli@...ebox.fr>
To:	linux-kernel@...r.kernel.org
Cc:	Richard Purdie <rpurdie@...ys.net>
Subject: [PATCH v2] LEDS: fix race between LED device uevent and actual attributes creation

If we were to dynamically register/unregister leds and have udev or other
daemons handle the leds class uevents, we would be notified of the adding of a
new LED and if the daemon immediately tries to open one of the attributes of
the led device, it would fail with a "no such file or directory" error since
this the attributes are not yet created. Fix this by switching attributes to be
class-wide, such that the driver core will register these attributes with
device_add_attrs and then emit the kobject_uevent ADD signal.

Signed-off-by:  Fainelli <ffainelli@...ebox.fr>
CC: stable@...nel.org
---
v2:
- make sure led_class_attrs size is known at compile time
- terminate led_class_attrs with a proper NULL terminator
- do not attempt to remove led device attributes twice

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 782f958..7b1bba2 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -72,11 +72,14 @@ static ssize_t led_max_brightness_show(struct device *dev,
 	return sprintf(buf, "%u\n", led_cdev->max_brightness);
 }
 
-static DEVICE_ATTR(brightness, 0644, led_brightness_show, led_brightness_store);
-static DEVICE_ATTR(max_brightness, 0444, led_max_brightness_show, NULL);
+static struct device_attribute led_class_attrs[] = {
+	__ATTR(brightness, 0644, led_brightness_show, led_brightness_store),
+	__ATTR(max_brightness, 0644, led_max_brightness_show, NULL),
 #ifdef CONFIG_LEDS_TRIGGERS
-static DEVICE_ATTR(trigger, 0644, led_trigger_show, led_trigger_store);
+	__ATTR(trigger, 0644, led_trigger_show, led_trigger_store),
 #endif
+	__ATTR_NULL,
+};
 
 /**
  * led_classdev_suspend - suspend an led_classdev.
@@ -127,18 +130,11 @@ static int led_resume(struct device *dev)
  */
 int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
 {
-	int rc;
-
 	led_cdev->dev = device_create(leds_class, parent, 0, led_cdev,
 				      "%s", led_cdev->name);
 	if (IS_ERR(led_cdev->dev))
 		return PTR_ERR(led_cdev->dev);
 
-	/* register the attributes */
-	rc = device_create_file(led_cdev->dev, &dev_attr_brightness);
-	if (rc)
-		goto err_out;
-
 #ifdef CONFIG_LEDS_TRIGGERS
 	init_rwsem(&led_cdev->trigger_lock);
 #endif
@@ -150,17 +146,9 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
 	if (!led_cdev->max_brightness)
 		led_cdev->max_brightness = LED_FULL;
 
-	rc = device_create_file(led_cdev->dev, &dev_attr_max_brightness);
-	if (rc)
-		goto err_out_attr_max;
-
 	led_update_brightness(led_cdev);
 
 #ifdef CONFIG_LEDS_TRIGGERS
-	rc = device_create_file(led_cdev->dev, &dev_attr_trigger);
-	if (rc)
-		goto err_out_led_list;
-
 	led_trigger_set_default(led_cdev);
 #endif
 
@@ -168,18 +156,8 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
 			led_cdev->name);
 
 	return 0;
-
-#ifdef CONFIG_LEDS_TRIGGERS
-err_out_led_list:
-	device_remove_file(led_cdev->dev, &dev_attr_max_brightness);
-#endif
-err_out_attr_max:
-	device_remove_file(led_cdev->dev, &dev_attr_brightness);
-	list_del(&led_cdev->node);
-err_out:
-	device_unregister(led_cdev->dev);
-	return rc;
 }
+
 EXPORT_SYMBOL_GPL(led_classdev_register);
 
 /**
@@ -190,10 +168,7 @@ EXPORT_SYMBOL_GPL(led_classdev_register);
  */
 void led_classdev_unregister(struct led_classdev *led_cdev)
 {
-	device_remove_file(led_cdev->dev, &dev_attr_max_brightness);
-	device_remove_file(led_cdev->dev, &dev_attr_brightness);
 #ifdef CONFIG_LEDS_TRIGGERS
-	device_remove_file(led_cdev->dev, &dev_attr_trigger);
 	down_write(&led_cdev->trigger_lock);
 	if (led_cdev->trigger)
 		led_trigger_set(led_cdev, NULL);
@@ -215,6 +190,7 @@ static int __init leds_init(void)
 		return PTR_ERR(leds_class);
 	leds_class->suspend = led_suspend;
 	leds_class->resume = led_resume;
+	leds_class->dev_attrs = led_class_attrs;
 	return 0;
 }
 




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