On 11/30/2016 09:22 AM, Jiada Wang wrote:
> From: Andreas Pape <apape@xxxxxxxxxxxxxx>
>
> Setting pointer and afterwards check for wrap around leads
> to the possibility of returning the inconsistent pointer position.
> This patch increments buffer pointer atomically to avoid this issue.
Makes sense.
>
> Signed-off-by: Andreas Pape <apape@xxxxxxxxxxxxxx>
> Signed-off-by: Jiada Wang <jiada_wang@xxxxxxxxxx>
> ---
> sound/core/pcm_dmaengine.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c
> index 8eb58c7..6f6da11 100644
> --- a/sound/core/pcm_dmaengine.c
> +++ b/sound/core/pcm_dmaengine.c
> @@ -139,12 +139,14 @@ EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_set_config_from_dai_data);
>
> static void dmaengine_pcm_dma_complete(void *arg)
> {
> + unsigned int new_pos;
> struct snd_pcm_substream *substream = arg;
> struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
>
> - prtd->pos += snd_pcm_lib_period_bytes(substream);
> - if (prtd->pos >= snd_pcm_lib_buffer_bytes(substream))
> - prtd->pos = 0;
> + new_pos = prtd->pos + snd_pcm_lib_period_bytes(substream);
> + if (new_pos >= snd_pcm_lib_buffer_bytes(substream))
> + new_pos = 0;
> + prtd->pos = new_pos;
But to really make it atomic I think this needs READ_ONCE/WRITE_ONCE.
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