Re: [PATCH v3] ALSA: compress: fix drain calls blocking other compress functions

[Vinod Koul <vinod.koul@intel.com>]

On Wed, Oct 30, 2013 at 03:47:45PM +0100, Takashi Iwai wrote:
> At Thu, 24 Oct 2013 16:37:31 +0530,
> Vinod Koul wrote:
> > 
> > The drain and drain_notify callback were blocked by low level driver untill the
> > draining was complete. Due to this being invoked with big fat mutex held, others
> > ops like reading timestamp, calling pause, drop were blocked.
> > 
> > So to fix this we add a new snd_compr_drain_notify() API. This would be required
> > to be invoked by low level driver when drain or partial drain has been completed
> > by the DSP. Thus we make the drain and partial_drain callback as non blocking
> > and driver returns immediately after notifying DSP.
> > The waiting is done while relasing the lock so that other ops can go ahead.
> > 
> > Signed-off-by: Vinod Koul <vinod.koul@intel.com>
> > CC: stable@vger.kernel.org
> > ---
> > v3:
> >  call snd_compr_drain_notify from compress_stop()
> >  rename draining -> drain_wake
> >  add some comments on state transistion after drain
> > 
> > v2:
> >  fix the 80 line warn
> >  move the state change to compress_drain()
> > 
> > 
> >  include/sound/compress_driver.h |   12 +++++++++++
> >  sound/core/compress_offload.c   |   41 ++++++++++++++++++++++++++++++++++++--
> >  2 files changed, 50 insertions(+), 3 deletions(-)
> > 
> > diff --git a/include/sound/compress_driver.h b/include/sound/compress_driver.h
> > index 9031a26..175ab32 100644
> > --- a/include/sound/compress_driver.h
> > +++ b/include/sound/compress_driver.h
> > @@ -48,6 +48,8 @@ struct snd_compr_ops;
> >   *	the ring buffer
> >   * @total_bytes_transferred: cumulative bytes transferred by offload DSP
> >   * @sleep: poll sleep
> > + * @wait: drain wait queue
> > + * @drain_wake: condition for drain wake
> >   */
> >  struct snd_compr_runtime {
> >  	snd_pcm_state_t state;
> > @@ -59,6 +61,8 @@ struct snd_compr_runtime {
> >  	u64 total_bytes_available;
> >  	u64 total_bytes_transferred;
> >  	wait_queue_head_t sleep;
> > +	wait_queue_head_t wait;
> > +	unsigned int drain_wake;
> >  	void *private_data;
> >  };
> >  
> > @@ -171,4 +175,12 @@ static inline void snd_compr_fragment_elapsed(struct snd_compr_stream *stream)
> >  	wake_up(&stream->runtime->sleep);
> >  }
> >  
> > +static inline void snd_compr_drain_notify(struct snd_compr_stream *stream)
> > +{
> > +	snd_BUG_ON(!stream);
> 
> Should return, otherwise you'll get Oops:
> 
> 	if (snd_BUG_ON(!stream))
> 		return;
ah, missed that!

> > +
> > +	stream->runtime->drain_wake = 1;
> > +	wake_up(&stream->runtime->wait);
> > +}
> > +
> >  #endif
> > diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
> > index bea523a..3eb47d0 100644
> > --- a/sound/core/compress_offload.c
> > +++ b/sound/core/compress_offload.c
> > @@ -123,6 +123,7 @@ static int snd_compr_open(struct inode *inode, struct file *f)
> >  	}
> >  	runtime->state = SNDRV_PCM_STATE_OPEN;
> >  	init_waitqueue_head(&runtime->sleep);
> > +	init_waitqueue_head(&runtime->wait);
> >  	data->stream.runtime = runtime;
> >  	f->private_data = (void *)data;
> >  	mutex_lock(&compr->lock);
> > @@ -682,12 +683,34 @@ static int snd_compr_stop(struct snd_compr_stream *stream)
> >  	if (!retval) {
> >  		stream->runtime->state = SNDRV_PCM_STATE_SETUP;
> >  		wake_up(&stream->runtime->sleep);
> > +		snd_compr_drain_notify(stream);
> >  		stream->runtime->total_bytes_available = 0;
> >  		stream->runtime->total_bytes_transferred = 0;
> >  	}
> >  	return retval;
> >  }
> >  
> > +static int snd_compress_wait_for_drain(struct snd_compr_stream *stream)
> > +{
> > +	/*
> > +	 * We are called with lock held. So drop the lock while we wait for
> > +	 * drain complete notfication from the driver
> > +	 *
> > +	 * It is expected that driver will notify the drain completion and then
> > +	 * stream will be moved to SETUP state, even if draining resulted in an
> > +	 * error. We can trigger next track after this.
> > +	 */
> > +	stream->runtime->state = SNDRV_PCM_STATE_DRAINING;
> > +	mutex_unlock(&stream->device->lock);
> > +
> > +	wait_event(stream->runtime->wait, stream->runtime->drain_wake);
> 
> Don't you really want the interruption?
> Or use wait_event_interruptible() and return error appropriately.
any interruption from usermode should trigger the compress_stop/compress_free
which will unblock this. I dont see the need to have interruptible here

> > +
> > +	wake_up(&stream->runtime->sleep);
> > +	mutex_lock(&stream->device->lock);
> > +
> > +	return 0;
> > +}
> > +
> >  static int snd_compr_drain(struct snd_compr_stream *stream)
> >  {
> >  	int retval;
> > @@ -695,11 +718,17 @@ static int snd_compr_drain(struct snd_compr_stream *stream)
> >  	if (stream->runtime->state == SNDRV_PCM_STATE_PREPARED ||
> >  			stream->runtime->state == SNDRV_PCM_STATE_SETUP)
> >  		return -EPERM;
> > +
> > +	stream->runtime->drain_wake = 0;
> >  	retval = stream->ops->trigger(stream, SND_COMPR_TRIGGER_DRAIN);
> > -	if (!retval) {
> > -		stream->runtime->state = SNDRV_PCM_STATE_DRAINING;
> > +	if (retval) {
> > +		pr_err("SND_COMPR_TRIGGER_DRAIN failed %d\n", retval);
> 
> I don't think spamming such an error is good.  The trigger error can
> happen often repeatedly once when it happens.  Such a message is at
> most a debug message, so use pr_debug(), if you still want to keep it
> in the core code.
Sure...

Thanks for the quick review, will send v4 before I hit the bed today!

--
~Vinod
> >  		wake_up(&stream->runtime->sleep);
> > +		return retval;
> >  	}
> > +
> > +	retval = snd_compress_wait_for_drain(stream);
> > +	stream->runtime->state = SNDRV_PCM_STATE_SETUP;
> >  	return retval;
> >  }
> >  
> > @@ -735,10 +764,16 @@ static int snd_compr_partial_drain(struct snd_compr_stream *stream)
> >  	if (stream->next_track == false)
> >  		return -EPERM;
> >  
> > +	stream->runtime->drain_wake = 0;
> >  	retval = stream->ops->trigger(stream, SND_COMPR_TRIGGER_PARTIAL_DRAIN);
> > +	if (retval) {
> > +		pr_err("Partial drain returned failure\n");
> 
> Ditto.
> 
> > +		wake_up(&stream->runtime->sleep);
> > +		return retval;
> > +	}
> >  
> >  	stream->next_track = false;
> > -	return retval;
> > +	return snd_compress_wait_for_drain(stream);
> >  }
> >  
> >  static long snd_compr_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
> > -- 
> > 1.7.0.4
> > 
> 
> 
> Takashi

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