void snd_pcm_period_elapsed(struct snd_pcm_substream *substream)
{
	struct snd_pcm_runtime *runtime;
	unsigned long flags;

	if (PCM_RUNTIME_CHECK(substream))
		return;
	runtime = substream->runtime;

	snd_pcm_stream_lock_irqsave(substream, flags);
	if (!snd_pcm_running(substream) ||
	    snd_pcm_update_hw_ptr0(substream, 1) < 0)
		goto _end;

#ifdef CONFIG_SND_PCM_TIMER
	if (substream->timer_running)
		snd_timer_interrupt(substream->timer, 1);
#endif
 _end:
	kill_fasync(&runtime->fasync, SIGIO, POLL_IN);
	snd_pcm_stream_unlock_irqrestore(substream, flags);
}
Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.