Initially the claim about no need for lock in brightness_show()
was valid as the function was just returning unchanged
LED brightness.
After the addition of led_update_brightness() this is no longer
true, as the function can change the brightness if a LED class
driver implements brightness_get op. It can lead to races between
led_update_brightness() and led_set_brightness().
Signed-off-by: Jacek Anaszewski <j.anaszewski@xxxxxxxxxxx>
Cc: Hans de Goede <hdegoede@xxxxxxxxxx>
Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
Cc: Pavel Machek <pavel@xxxxxx>
Cc: Andrew Lunn <andrew@xxxxxxx>
---
Changes since v1:
- added led_sysfs_is_disabled() check
- moved sprintf under mutex protection
drivers/leds/led-class.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index b12f861..e472407 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -29,11 +29,23 @@ static ssize_t brightness_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct led_classdev *led_cdev = dev_get_drvdata(dev);
+ int ret;
- /* no lock needed for this */
- led_update_brightness(led_cdev);
+ mutex_lock(&led_cdev->led_access);
+
+ if (led_sysfs_is_disabled(led_cdev)) {
+ ret = -EBUSY;
+ goto unlock;
+ }
+
+ ret = led_update_brightness(led_cdev);
+ if (ret < 0)
+ goto unlock;
- return sprintf(buf, "%u\n", led_cdev->brightness);
+ ret = sprintf(buf, "%u\n", led_cdev->brightness);
+unlock:
+ mutex_unlock(&led_cdev->led_access);
+ return ret;
}
static ssize_t brightness_store(struct device *dev,
--
1.9.1
--
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