4.4-stable review patch. If anyone has any objections, please let me know.
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From: Milo Kim milo.kim@ti.com
commit d1aa577f5e191d77d3ad62da93729b5af9532bb4 upstream.
Workqueue, 'set_brightness_work' is used for scheduling brightness control. This workqueue is canceled when the LED class device is unregistered. Currently, LED subsystem handles like below.
cancel_work_sync(&led_cdev->set_brightness_work) led_set_brightness(led_cdev, LED_OFF)
However, this could be a problem. Workqueue is going to be canceled but LED device needs to be off. The worst case is null pointer access due to scheduling a workqueue.
LED module is loaded. LED driver private data is allocated by using devm_zalloc().
LED module is unloaded. led_classdev_unregister() is called. cancel_work_sync() led_set_brightness(led_cdev, LED_OFF) schedule_work() if LED driver uses brightness_set_blocking() In the meantime, driver private data will be freed.
..scheduling..
brightness_set_blocking() callback is invoked. For the brightness control, LED driver tries to access private data but resource is removed!
To avoid this problem, LED subsystem should turn off the brightness first and wait for completion.
led_set_brightness(led_cdev, LED_OFF) flush_work(&led_cdev->set_brightness_work)
It guarantees that LED driver turns off the brightness prior to resource management.
Cc: linux-leds@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Milo Kim milo.kim@ti.com Signed-off-by: Jacek Anaszewski j.anaszewski@samsung.com Signed-off-by: Krzysztof Kozlowski krzk@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/leds/led-class.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
--- a/drivers/leds/led-class.c +++ b/drivers/leds/led-class.c @@ -247,12 +247,13 @@ void led_classdev_unregister(struct led_ up_write(&led_cdev->trigger_lock); #endif
- cancel_work_sync(&led_cdev->set_brightness_work); - /* Stop blinking */ led_stop_software_blink(led_cdev); + led_set_brightness(led_cdev, LED_OFF);
+ flush_work(&led_cdev->set_brightness_work); + device_unregister(led_cdev->dev);
down_write(&leds_list_lock);