There is a small window during probing when IO is running but the backlight is not registered. Processing events during that time will crash. The completion handler needs to check for a backlight before scheduling work.
The bug is as old as the driver.
Signed-off-by: Oliver Neukum oneukum@suse.com CC: stable@vger.kernel.org --- drivers/usb/misc/appledisplay.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c index c8098e9b432e..62b5a30edc42 100644 --- a/drivers/usb/misc/appledisplay.c +++ b/drivers/usb/misc/appledisplay.c @@ -107,7 +107,12 @@ static void appledisplay_complete(struct urb *urb) case ACD_BTN_BRIGHT_UP: case ACD_BTN_BRIGHT_DOWN: pdata->button_pressed = 1; - schedule_delayed_work(&pdata->work, 0); + /* + * there is a window during which no device + * is registered + */ + if (pdata->bd ) + schedule_delayed_work(&pdata->work, 0); break; case ACD_BTN_NONE: default: @@ -202,6 +207,7 @@ static int appledisplay_probe(struct usb_interface *iface, const struct usb_device_id *id) { struct backlight_properties props; + struct backlight_device *backlight; struct appledisplay *pdata; struct usb_device *udev = interface_to_usbdev(iface); struct usb_endpoint_descriptor *endpoint; @@ -272,13 +278,14 @@ static int appledisplay_probe(struct usb_interface *iface, memset(&props, 0, sizeof(struct backlight_properties)); props.type = BACKLIGHT_RAW; props.max_brightness = 0xff; - pdata->bd = backlight_device_register(bl_name, NULL, pdata, + backlight = backlight_device_register(bl_name, NULL, pdata, &appledisplay_bl_data, &props); - if (IS_ERR(pdata->bd)) { + if (IS_ERR(backlight)) { dev_err(&iface->dev, "Backlight registration failed\n"); - retval = PTR_ERR(pdata->bd); + retval = PTR_ERR(backlight); goto error; } + pdata->bd = backlight;
/* Try to get brightness */ brightness = appledisplay_bl_get_brightness(pdata->bd);