[bug report] media: sound/usb: Use Media Controller API to share media resources

[Dan Carpenter]

Hello Shuah Khan,

The patch 66354f18fe5f: "media: sound/usb: Use Media Controller API
to share media resources" from Apr 1, 2019, leads to the following
static checker warning:

	sound/usb/media.c:287 snd_media_device_create()
	warn: 'mdev' can also be NULL

sound/usb/media.c
   270  
   271          mdev = media_device_usb_allocate(usbdev, KBUILD_MODNAME, THIS_MODULE);
                ^^^^

If CONFIG_MEDIA_CONTROLLER is disabled then "mdev" is NULL.

   272          if (IS_ERR(mdev))
   273                  return -ENOMEM;
   274  
   275          /* save media device - avoid lookups */
   276          chip->media_dev = mdev;
   277  
   278  snd_mixer_init:
   279          /* Create media entities for mixer and control dev */
   280          ret = snd_media_mixer_init(chip);
   281          /* media_device might be registered, print error and continue */
   282          if (ret)
   283                  dev_err(&usbdev->dev,
   284                          "Couldn't create media mixer entities. Error: %d\n",
   285                          ret);
   286  
   287          if (!media_devnode_is_registered(mdev->devnode)) {
                                                 ^^^^^^^^^^^^^
dereferenced without checking here

   288                  /* dont'register if snd_media_mixer_init() failed */
   289                  if (ret)
   290                          goto create_fail;
   291  
   292                  /* register media_device */
   293                  ret = media_device_register(mdev);
   294  create_fail:
   295                  if (ret) {
   296                          snd_media_mixer_delete(chip);
   297                          media_device_delete(mdev, KBUILD_MODNAME, THIS_MODULE);
   298                          /* clear saved media_dev */
   299                          chip->media_dev = NULL;
   300                          dev_err(&usbdev->dev,
   301                                  "Couldn't register media device. Error: %d\n",
   302                                  ret);
   303                          return ret;
   304                  }
   305          }
   306  
   307          return ret;
   308  }

regards,
dan carpenter