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Subject[PATCH v1 1/2] ASoC: rsnd: ssi: fix race condition in rsnd_ssi_pointer_update
Date
From: Jiada Wang <jiada_wang@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_wang@mentor.com>
Reviewed-by: Takashi Sakamoto <takashi.sakamoto@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

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