snd_BUG_ON() macro is similar with WARN_ON() macro. For example,

  snd_BUG_ON(!pointer);

          

or it can be used as the condition,

  if (snd_BUG_ON(non_zero_is_bug))
          return -EINVAL;

          

The macro takes an conditional expression to evaluate. When CONFIG_SND_DEBUG, is set, if the expression is non-zero, it shows the warning message such as BUG? (xxx) normally followed by stack trace. In both cases it returns the evaluated value.