On 12/01/2016 06:24 AM, Jiada Wang wrote:

From: Andreas Pape apape@de.adit-jv.com

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@de.adit-jv.com Signed-off-by: Jiada Wang jiada_wang@mentor.com

Thanks for the patch. Looks good to me.

Reviewed-by: Lars-Peter Clausen lars@metafoo.de

---

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);