static inline struct obd_device* chlg_obd_get(struct chlg_registered_dev *dev)
{
      struct obd_device *obd;
      mutex_lock(&chlg_registered_dev_lock);
      if (list_empty(&dev->ced_obds))
          return NULL;              // <-- mutex not released
      ...
      mutex_unlock(&chlg_registered_dev_lock);
      return obd;
}