Re: [PATCH v3 3/3] ALSA: compress: fix partial_drain completion state

[Charles Keepax]

On Thu, Jun 25, 2020 at 09:16:51PM +0530, Vinod Koul wrote:
> On partial_drain completion we should be in SNDRV_PCM_STATE_RUNNING
> state, so set that for partially draining streams in
> snd_compr_drain_notify() and use a flag for partially draining streams
> 
> While at it, add locks for stream state change in
> snd_compr_drain_notify() as well.
> 
> Fixes: f44f2a5417b2 ("ALSA: compress: fix drain calls blocking other compress functions (v6)")
> Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> Tested-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> Signed-off-by: Vinod Koul <vkoul@xxxxxxxxxx>
> ---
> @@ -187,7 +189,15 @@ static inline void snd_compr_drain_notify(struct snd_compr_stream *stream)
>  	if (snd_BUG_ON(!stream))
>  		return;
>  
> -	stream->runtime->state = SNDRV_PCM_STATE_SETUP;
> +	mutex_lock(&stream->device->lock);
> +	/* for partial_drain case we are back to running state on success */
> +	if (stream->partial_drain) {
> +		stream->runtime->state = SNDRV_PCM_STATE_RUNNING;
> +		stream->partial_drain = false; /* clear this flag as well */
> +	} else {
> +		stream->runtime->state = SNDRV_PCM_STATE_SETUP;
> +	}
> +	mutex_unlock(&stream->device->lock);

You have added locking here in snd_compr_drain_notify but....
>  
>  	wake_up(&stream->runtime->sleep);
>  }
> diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
> index e618580feac4..1c4b2cf450a0 100644
> --- a/sound/core/compress_offload.c
> +++ b/sound/core/compress_offload.c
> @@ -803,6 +803,9 @@ static int snd_compr_stop(struct snd_compr_stream *stream)
>  
>  	retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_STOP);
>  	if (!retval) {
> +		/* clear flags and stop any drain wait */
> +		stream->partial_drain = false;
> +		stream->metadata_set = false;
>  		snd_compr_drain_notify(stream);

that can be called from snd_compr_stop here which is already
holding the lock resulting in deadlock.

Thanks,
Charles