On 12/01/2016 06:24 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 accesses buffer pointer atomically to avoid this issue.
>
> v2: use READ_ONCE and WRITE_ONCE to ensure read/write of buffer pointer in
> only one access
> also updates snd_dmaengine_pcm_pointer_no_residue to ensure atomic
> access
>
> Signed-off-by: Andreas Pape <apape@xxxxxxxxxxxxxx>
> Signed-off-by: Jiada Wang <jiada_wang@xxxxxxxxxx>
Thanks for the patch. Looks good to me.
Reviewed-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
> ---
> sound/core/pcm_dmaengine.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c
> index 8eb58c7..b6255fd 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;
> + WRITE_ONCE(prtd->pos, new_pos);
>
> snd_pcm_period_elapsed(substream);
> }
> @@ -235,7 +237,7 @@ EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_trigger);
> snd_pcm_uframes_t snd_dmaengine_pcm_pointer_no_residue(struct snd_pcm_substream *substream)
> {
> struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
> - return bytes_to_frames(substream->runtime, prtd->pos);
> + return bytes_to_frames(substream->runtime, READ_ONCE(prtd->pos));
> }
> EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_pointer_no_residue);
>
>
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