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ASoC: dpcm: Fix race between FE/BE updates and trigger
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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>
Cc: stable@vger.kernel.org
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Takashi Iwai authored and Mark Brown committed Nov 4, 2014
1 parent f114040 commit ea9d0d7
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Showing 2 changed files with 58 additions and 16 deletions.
2 changes: 2 additions & 0 deletions include/sound/soc-dpcm.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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 */
Expand Down
72 changes: 56 additions & 16 deletions sound/soc/soc-pcm.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1522,13 +1522,36 @@ static void dpcm_set_fe_runtime(struct snd_pcm_substream *substream)
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) {
Expand All @@ -1550,13 +1573,13 @@ static int dpcm_fe_dai_startup(struct snd_pcm_substream *fe_substream)
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;
}

Expand Down Expand Up @@ -1603,7 +1626,7 @@ static int dpcm_fe_dai_shutdown(struct snd_pcm_substream *substream)
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);
Expand All @@ -1617,7 +1640,7 @@ static int dpcm_fe_dai_shutdown(struct snd_pcm_substream *substream)
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;
}

Expand Down Expand Up @@ -1665,7 +1688,7 @@ static int dpcm_fe_dai_hw_free(struct snd_pcm_substream *substream)
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);

Expand All @@ -1680,7 +1703,7 @@ static int dpcm_fe_dai_hw_free(struct snd_pcm_substream *substream)
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;
Expand Down Expand Up @@ -1773,7 +1796,7 @@ static int dpcm_fe_dai_hw_params(struct snd_pcm_substream *substream,
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));
Expand All @@ -1796,7 +1819,7 @@ static int dpcm_fe_dai_hw_params(struct snd_pcm_substream *substream,
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;
}
Expand Down Expand Up @@ -1910,7 +1933,7 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
}
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;
Expand Down Expand Up @@ -1984,6 +2007,23 @@ static int dpcm_fe_dai_trigger(struct snd_pcm_substream *substream, int cmd)
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;
Expand Down Expand Up @@ -2027,7 +2067,7 @@ static int dpcm_fe_dai_prepare(struct snd_pcm_substream *substream)

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)) {
Expand All @@ -2054,7 +2094,7 @@ static int dpcm_fe_dai_prepare(struct snd_pcm_substream *substream)
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;
Expand Down Expand Up @@ -2201,11 +2241,11 @@ static int dpcm_run_new_update(struct snd_soc_pcm_runtime *fe, int stream)
{
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;
}
Expand All @@ -2214,11 +2254,11 @@ static int dpcm_run_old_update(struct snd_soc_pcm_runtime *fe, int stream)
{
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;
}
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