Re: [PATCH] pcm: dmix: fix incorrect boundary handling in snd_pcm_dmix_sync_area

On Fri, 15 May 2020 18:24:08 +0200, Maarten Baert wrote:

The available size calculation did not handle wraparound correctly. Also, the underrun handling code confused slave_buffer_size with slave_boundary, causing another integer overflow that results in too many samples being skipped.

Signed-off-by: Maarten Baert maarten-baert@hotmail.com

Thanks, the code change looks correct but the embedded patch isn't applicable. Indeed the patch seems somehow malformed.

Could you repost the proper one, at best with git-send-email?

thanks,

Takashi

---

src/pcm/pcm_dmix.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/src/pcm/pcm_dmix.c b/src/pcm/pcm_dmix.c index 843fa316..b5fdb240 100644 --- a/src/pcm/pcm_dmix.c +++ b/src/pcm/pcm_dmix.c @@ -315,11 +315,12 @@ static void snd_pcm_dmix_sync_area(snd_pcm_t *pcm) /* check the available size in the local buffer * last_appl_ptr keeps the last updated position */

• size = dmix->appl_ptr - dmix->last_appl_ptr;

• if (dmix->appl_ptr >= dmix->last_appl_ptr)

• size = dmix->appl_ptr - dmix->last_appl_ptr;
  

• else

• size = dmix->appl_ptr + (pcm->boundary - dmix->last_appl_ptr);
  

  if (! size) return;

• if (size >= pcm->boundary / 2)

• size = pcm->boundary - size;
  

  /* the slave_app_ptr can be far behind the slave_hw_ptr */ /* reduce mixing and errors here - just skip not catched writes */

@@ -328,18 +329,19 @@ static void snd_pcm_dmix_sync_area(snd_pcm_t *pcm) else slave_size = dmix->slave_appl_ptr + (dmix->slave_boundary - dmix->slave_hw_ptr); if (slave_size > dmix->slave_buffer_size) {

• transfer = dmix->slave_buffer_size - slave_size;
  

• transfer = dmix->slave_boundary - slave_size;
  

  if (transfer > size) transfer = size; dmix->last_appl_ptr += transfer; dmix->last_appl_ptr %= pcm->boundary; dmix->slave_appl_ptr += transfer; dmix->slave_appl_ptr %= dmix->slave_boundary;

• size = dmix->appl_ptr - dmix->last_appl_ptr;
  

• if (dmix->appl_ptr >= dmix->last_appl_ptr)
  

• 	size = dmix->appl_ptr - dmix->last_appl_ptr;
  

• else
  

• 	size = dmix->appl_ptr + (pcm->boundary - dmix->last_appl_ptr);
  

  if (! size) return;

• if (size >= pcm->boundary / 2)
  

• 	size = pcm->boundary - size;
  

  } /* check the available size in the slave PCM buffer */

-- 2.26.2