[PATCH v1 1/2] ASoC: rsnd: ssi: fix race condition in rsnd_ssi_pointer_update

[jiada_wang]

From: Jiada Wang <jiada_w...@mentor.com>

Currently there is race condition between set of byte_pos and wrap
it around when new buffer starts. If .pointer is called in-between
it will result in inconsistent pointer position be returned
from .pointer callback.

This patch increments buffer pointer atomically to avoid this issue.

Signed-off-by: Jiada Wang <jiada_w...@mentor.com>
Reviewed-by: Takashi Sakamoto <takashi.sakam...@miraclelinux.com>
---
 sound/soc/sh/rcar/ssi.c |   16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/sound/soc/sh/rcar/ssi.c b/sound/soc/sh/rcar/ssi.c
index fece1e5f..cbf3bf3 100644
--- a/sound/soc/sh/rcar/ssi.c
+++ b/sound/soc/sh/rcar/ssi.c
@@ -446,25 +446,29 @@ static bool rsnd_ssi_pointer_update(struct rsnd_mod *mod,
                                    int byte)
 {
        struct rsnd_ssi *ssi = rsnd_mod_to_ssi(mod);
+       bool ret = false;
+       int byte_pos;
 
-       ssi->byte_pos += byte;
+       byte_pos = ssi->byte_pos + byte;
 
-       if (ssi->byte_pos >= ssi->next_period_byte) {
+       if (byte_pos >= ssi->next_period_byte) {
                struct snd_pcm_runtime *runtime = rsnd_io_to_runtime(io);
 
                ssi->period_pos++;
                ssi->next_period_byte += ssi->byte_per_period;
 
                if (ssi->period_pos >= runtime->periods) {
-                       ssi->byte_pos = 0;
+                       byte_pos = 0;
                        ssi->period_pos = 0;
                        ssi->next_period_byte = ssi->byte_per_period;
                }
 
-               return true;
+               ret = true;
        }
 
-       return false;
+       WRITE_ONCE(ssi->byte_pos, byte_pos);
+
+       return ret;
 }
 
 /*
@@ -838,7 +842,7 @@ static int rsnd_ssi_pointer(struct rsnd_mod *mod,
        struct rsnd_ssi *ssi = rsnd_mod_to_ssi(mod);
        struct snd_pcm_runtime *runtime = rsnd_io_to_runtime(io);
 
-       *pointer = bytes_to_frames(runtime, ssi->byte_pos);
+       *pointer = bytes_to_frames(runtime, READ_ONCE(ssi->byte_pos));
 
        return 0;
 }
-- 
1.7.9.5