[PATCH 3.14 27/73] ASoC: dpcm: Fix race between FE/BE updates and trigger

Greg Kroah-Hartman
2014-12-05T23:26:14Z

From: Takashi Iwai <tiwai@suse.de>

commit ea9d0d771fcd32cd56070819749477d511ec9117 upstream.

DPCM can update the FE/BE connection states totally asynchronously
from the FE's PCM state. Most of FE/BE state changes are protected by
mutex, so that they won't race, but there are still some actions that
are uncovered. For example, suppose to switch a BE while a FE's
stream is running. This would call soc_dpcm_runtime_update(), which
sets FE's runtime_update flag, then sets up and starts BEs, and clears
FE's runtime_update flag again.

When a device emits XRUN during this operation, the PCM core triggers
snd_pcm_stop(XRUN). Since the trigger action is an atomic ops, this
isn't blocked by the mutex, thus it kicks off DPCM's trigger action.
It eventually updates and clears FE's runtime_update flag while
soc_dpcm_runtime_update() is running concurrently, and it results in
confusion.

Usually, for avoiding such a race, we take a lock. There is a PCM
stream lock for that purpose. However, as already mentioned, the
trigger action is atomic, and we can't take the lock for the whole
soc_dpcm_runtime_update() or other operations that include the lengthy
jobs like hw_params or prepare.

This patch provides an alternative solution. This adds a way to defer
the conflicting trigger callback to be executed at the end of FE/BE
state changes. For doing it, two things are introduced:

- Each runtime_update state change of FEs is protected via PCM stream
lock.
- The FE's trigger callback checks the runtime_update flag. If it's
not set, the trigger action is executed there. If set, mark the
pending trigger action and returns immediately.
- At the exit of runtime_update state change, it checks whether the
pending trigger is present. If yes, it executes the trigger action
at this point.

Reported-and-tested-by: Qiao Zhou <zhouqiao@marvell.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Acked-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/sound/soc-dpcm.h | 2 +
sound/soc/soc-pcm.c | 72 ++++++++++++++++++++++++++++++++++++-----------
2 files changed, 58 insertions(+), 16 deletions(-)

--- a/include/sound/soc-dpcm.h
+++ b/include/sound/soc-dpcm.h
@@ -102,6 +102,8 @@ struct snd_soc_dpcm_runtime {
/* state and update */
enum snd_soc_dpcm_update runtime_update;
enum snd_soc_dpcm_state state;
+
+ int trigger_pending; /* trigger cmd + 1 if pending, 0 if not */
};

/* can this BE stop and free */
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -1258,13 +1258,36 @@ static void dpcm_set_fe_runtime(struct s
dpcm_init_runtime_hw(runtime, &cpu_dai_drv->capture);
}

+static int dpcm_fe_dai_do_trigger(struct snd_pcm_substream *substream, int cmd);
+
+/* Set FE's runtime_update state; the state is protected via PCM stream lock
+ * for avoiding the race with trigger callback.
+ * If the state is unset and a trigger is pending while the previous operation,
+ * process the pending trigger action here.
+ */
+static void dpcm_set_fe_update_state(struct snd_soc_pcm_runtime *fe,
+ int stream, enum snd_soc_dpcm_update state)
+{
+ struct snd_pcm_substream *substream =
+ snd_soc_dpcm_get_substream(fe, stream);
+
+ snd_pcm_stream_lock_irq(substream);
+ if (state == SND_SOC_DPCM_UPDATE_NO && fe->dpcm[stream].trigger_pending) {
+ dpcm_fe_dai_do_trigger(substream,
+ fe->dpcm[stream].trigger_pending - 1);
+ fe->dpcm[stream].trigger_pending = 0;
+ }
+ fe->dpcm[stream].runtime_update = state;
+ snd_pcm_stream_unlock_irq(substream);
+}
+
static int dpcm_fe_dai_startup(struct snd_pcm_substream *fe_substream)
{
struct snd_soc_pcm_runtime *fe = fe_substream->private_data;
struct snd_pcm_runtime *runtime = fe_substream->runtime;
int stream = fe_substream->stream, ret = 0;

- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_FE;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_FE);

ret = dpcm_be_dai_startup(fe, fe_substream->stream);
if (ret < 0) {
@@ -1286,13 +1309,13 @@ static int dpcm_fe_dai_startup(struct sn
dpcm_set_fe_runtime(fe_substream);
snd_pcm_limit_hw_rates(runtime);

- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_NO;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_NO);
return 0;

unwind:
dpcm_be_dai_startup_unwind(fe, fe_substream->stream);
be_err:
- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_NO;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_NO);
return ret;
}

@@ -1339,7 +1362,7 @@ static int dpcm_fe_dai_shutdown(struct s
struct snd_soc_pcm_runtime *fe = substream->private_data;
int stream = substream->stream;

- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_FE;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_FE);

/* shutdown the BEs */
dpcm_be_dai_shutdown(fe, substream->stream);
@@ -1353,7 +1376,7 @@ static int dpcm_fe_dai_shutdown(struct s
dpcm_dapm_stream_event(fe, stream, SND_SOC_DAPM_STREAM_STOP);

fe->dpcm[stream].state = SND_SOC_DPCM_STATE_CLOSE;
- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_NO;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_NO);
return 0;
}

@@ -1401,7 +1424,7 @@ static int dpcm_fe_dai_hw_free(struct sn
int err, stream = substream->stream;

mutex_lock_nested(&fe->card->mutex, SND_SOC_CARD_CLASS_RUNTIME);
- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_FE;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_FE);

dev_dbg(fe->dev, "ASoC: hw_free FE %s\n", fe->dai_link->name);

@@ -1416,7 +1439,7 @@ static int dpcm_fe_dai_hw_free(struct sn
err = dpcm_be_dai_hw_free(fe, stream);

fe->dpcm[stream].state = SND_SOC_DPCM_STATE_HW_FREE;
- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_NO;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_NO);

mutex_unlock(&fe->card->mutex);
return 0;
@@ -1509,7 +1532,7 @@ static int dpcm_fe_dai_hw_params(struct
int ret, stream = substream->stream;

mutex_lock_nested(&fe->card->mutex, SND_SOC_CARD_CLASS_RUNTIME);
- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_FE;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_FE);

memcpy(&fe->dpcm[substream->stream].hw_params, params,
sizeof(struct snd_pcm_hw_params));
@@ -1532,7 +1555,7 @@ static int dpcm_fe_dai_hw_params(struct
fe->dpcm[stream].state = SND_SOC_DPCM_STATE_HW_PARAMS;

out:
- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_NO;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_NO);
mutex_unlock(&fe->card->mutex);
return ret;
}
@@ -1646,7 +1669,7 @@ int dpcm_be_dai_trigger(struct snd_soc_p
}
EXPORT_SYMBOL_GPL(dpcm_be_dai_trigger);

-static int dpcm_fe_dai_trigger(struct snd_pcm_substream *substream, int cmd)
+static int dpcm_fe_dai_do_trigger(struct snd_pcm_substream *substream, int cmd)
{
struct snd_soc_pcm_runtime *fe = substream->private_data;
int stream = substream->stream, ret;
@@ -1720,6 +1743,23 @@ out:
return ret;
}

+static int dpcm_fe_dai_trigger(struct snd_pcm_substream *substream, int cmd)
+{
+ struct snd_soc_pcm_runtime *fe = substream->private_data;
+ int stream = substream->stream;
+
+ /* if FE's runtime_update is already set, we're in race;
+ * process this trigger later at exit
+ */
+ if (fe->dpcm[stream].runtime_update != SND_SOC_DPCM_UPDATE_NO) {
+ fe->dpcm[stream].trigger_pending = cmd + 1;
+ return 0; /* delayed, assuming it's successful */
+ }
+
+ /* we're alone, let's trigger */
+ return dpcm_fe_dai_do_trigger(substream, cmd);
+}
+
int dpcm_be_dai_prepare(struct snd_soc_pcm_runtime *fe, int stream)
{
struct snd_soc_dpcm *dpcm;
@@ -1763,7 +1803,7 @@ static int dpcm_fe_dai_prepare(struct sn

dev_dbg(fe->dev, "ASoC: prepare FE %s\n", fe->dai_link->name);

- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_FE;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_FE);

/* there is no point preparing this FE if there are no BEs */
if (list_empty(&fe->dpcm[stream].be_clients)) {
@@ -1790,7 +1830,7 @@ static int dpcm_fe_dai_prepare(struct sn
fe->dpcm[stream].state = SND_SOC_DPCM_STATE_PREPARE;

out:
- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_NO;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_NO);
mutex_unlock(&fe->card->mutex);

return ret;
@@ -1937,11 +1977,11 @@ static int dpcm_run_new_update(struct sn
{
int ret;

- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_BE;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_BE);
ret = dpcm_run_update_startup(fe, stream);
if (ret < 0)
dev_err(fe->dev, "ASoC: failed to startup some BEs\n");
- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_NO;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_NO);

return ret;
}
@@ -1950,11 +1990,11 @@ static int dpcm_run_old_update(struct sn
{
int ret;

- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_BE;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_BE);
ret = dpcm_run_update_shutdown(fe, stream);
if (ret < 0)
dev_err(fe->dev, "ASoC: failed to shutdown some BEs\n");
- fe->dpcm[stream].runtime_update = SND_SOC_DPCM_UPDATE_NO;
+ dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_NO);

return ret;
}