[alsa-devel] [PATCH] PCM: snd_pcm_dmix_drain() maybe blocked after suspend and resume

[Takashi Iwai]

At Tue, 9 Jun 2015 10:35:41 +0800,
Shengjiu Wang wrote:
> 
> On Mon, Jun 08, 2015 at 01:31:41PM +0200, Takashi Iwai wrote:
> > At Mon, 8 Jun 2015 17:38:11 +0800,
> > Shengjiu Wang wrote:
> > > 
> > > After suspend and resume, the alsa driver is stopped. But if alsa-lib run
> > > into snd_pcm_dmix_drain(), it need to wait avail >= pcm->stop_threshold,
> > > otherwise, it will not exit the loop, so finally it is blocked at poll() of
> > > snd_pcm_wait_nocheck(pcm, -1).
> > > This patch is to add state check after snd_pcm_wait_nocheck(pcm, -1), if
> > > the state is SND_PCM_STATE_SUSPENDED, then return error.
> > > 
> > > Signed-off-by: Shengjiu Wang <shengjiu.wang at freescale.com>
> > > ---
> > >  src/pcm/pcm_dmix.c |    6 ++++++
> > >  1 file changed, 6 insertions(+)
> > > 
> > > diff --git a/src/pcm/pcm_dmix.c b/src/pcm/pcm_dmix.c
> > > index babde6a..0cc318e 100644
> > > --- a/src/pcm/pcm_dmix.c
> > > +++ b/src/pcm/pcm_dmix.c
> > > @@ -647,6 +647,12 @@ static int snd_pcm_dmix_drain(snd_pcm_t *pcm)
> > >  		if (dmix->state == SND_PCM_STATE_DRAINING) {
> > >  			snd_pcm_dmix_sync_area(pcm);
> > >  			snd_pcm_wait_nocheck(pcm, -1);
> > > +			switch (snd_pcm_state(pcm)) {
> > 
> > It's better (shorter) to call snd_pcm_state(dmix->spcm) in this case.
> > 
> > And, I think we should have the check of SND_PCM_STATE_SUSPENDED at
> > the beginning of snd_pcm_dmix_drain() before entering to the loop,
> > too.
> > 
> > Last but not least, the very same bug is present for dshare.  Could
> > you fix this together?
> > 
> Ok, I will refine the patch. But one thing I don't understand is that why need
> to check the SND_PCM_STATE_SUSPENDED before entering the loop, seems check the
> state in the loop can resolve the issue.

It's just a minor optimization.  The check isn't done at the beginning
of the loop but after a few other calls (sync_ptr and sync_area) to be
skipped at PM.


Takashi