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leds: turn off the LED and wait for completion on unregistering LED class device

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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>
This commit is contained in:
Milo Kim 2015-11-20 17:03:00 +09:00 committed by Jacek Anaszewski
parent abc196359b
commit d1aa577f5e
1 changed files with 3 additions and 2 deletions
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5
drivers/leds/led-class.c
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@ -245,12 +245,13 @@ void led_classdev_unregister(struct led_classdev *led_cdev)
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);