[alsa-devel] [PATCH v3] ALSA: compress: fix drain calls blocking other compress functions

[Takashi Iwai]

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 at intel.com>
> CC: stable at 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;

> +
> +	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.

> +
> +	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.

>  		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