[alsa-devel] [patch] snd_pcm_drain and lock-ups

[Mike Gorse]

On Fri, 21 Sep 2007, Jaroslav Kysela wrote:

>> I posted last week because I am getting lockups when portaudio calls
>> snd_pcm_drain, and snd_pcm_rate_drain calls snd_pcm_wait on its slave.
>>
>> Now that I've looked at this more, I'm seeing that it involves dmix, since
>> a dmix plugin is behind the rate plugin.
>>
>> The dmix code in alsa-lib is setting a xrun state because
>> snd_pcm_mmap_playback_avail returns a large value.
>>
>> snd_pcm_wait is then called on the slave of the rate pcm, which is a pcm
>> with a type of SND_PCM_TYPE_ROUTE whose slave is the dmix, but the route
>> pcm is returning a different value for snd_pcm_mmap_avail than the dmix
>> pcm, so it is not triggering snd_pcm_wait to check for a xrun.
>>
> I think that better fix is to change the code in snd_pcm_rate_drain(). You
> can set avail_min to 1 there, so condition in snd_pcm_wait() will match.
>
> Does this patch help?
>
> diff -r 68d71239d651 src/pcm/pcm_rate.c
> --- a/src/pcm/pcm_rate.c	Thu Sep 20 13:20:03 2007 +0200
> +++ b/src/pcm/pcm_rate.c	Fri Sep 21 10:14:41 2007 +0200
> @@ -1076,10 +1076,10 @@ static int snd_pcm_rate_drain(snd_pcm_t
> 		snd_pcm_uframes_t size, ofs, saved_avail_min;
> 		snd_pcm_sw_params_t sw_params;
>
> -		/* temporarily set avail_min to one period */
> +		/* temporarily set avail_min to one */
> 		sw_params = rate->sw_params;
> 		saved_avail_min = sw_params.avail_min;
> -		sw_params.avail_min = rate->gen.slave->period_size;
> +		sw_params.avail_min = 1;
> 		snd_pcm_sw_params(rate->gen.slave, &sw_params);
>
> 		size = rate->appl_ptr - rate->last_commit_ptr;
>
> 						Jaroslav

Yes, that also works.

Thanks,
-Mike