• Milo Kim's avatar
    leds: turn off the LED and wait for completion on unregistering LED class device · d1aa577f
    Milo Kim authored
    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: default avatarMilo Kim <milo.kim@ti.com>
    Signed-off-by: default avatarJacek Anaszewski <j.anaszewski@samsung.com>
    d1aa577f
led-class.c 7.74 KB