[alsa-devel] [PATCH 1/4] ALSA: PCM: Fix some races at disconnection

[Takashi Iwai]

Fix races at PCM disconnection:
- while a PCM device is being opened or closed
- while the PCM state is being changed without lock in prepare,
  hw_params, hw_free ops

Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/core/pcm.c        |  7 ++++++-
 sound/core/pcm_native.c | 16 ++++++++++++----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/sound/core/pcm.c b/sound/core/pcm.c
index f299194..993b240 100644
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -1086,11 +1086,15 @@ static int snd_pcm_dev_disconnect(struct snd_device *device)
 	if (list_empty(&pcm->list))
 		goto unlock;
 
+	mutex_lock(&pcm->open_mutex);
 	list_del_init(&pcm->list);
 	for (cidx = 0; cidx < 2; cidx++)
-		for (substream = pcm->streams[cidx].substream; substream; substream = substream->next)
+		for (substream = pcm->streams[cidx].substream; substream; substream = substream->next) {
+			snd_pcm_stream_lock_irq(substream);
 			if (substream->runtime)
 				substream->runtime->status->state = SNDRV_PCM_STATE_DISCONNECTED;
+			snd_pcm_stream_unlock_irq(substream);
+		}
 	list_for_each_entry(notify, &snd_pcm_notify_list, list) {
 		notify->n_disconnect(pcm);
 	}
@@ -1110,6 +1114,7 @@ static int snd_pcm_dev_disconnect(struct snd_device *device)
 			pcm->streams[cidx].chmap_kctl = NULL;
 		}
 	}
+	mutex_unlock(&pcm->open_mutex);
  unlock:
 	mutex_unlock(&register_mutex);
 	return 0;
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 5e12e5b..8753c89 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -369,6 +369,14 @@ static int period_to_usecs(struct snd_pcm_runtime *runtime)
 	return usecs;
 }
 
+static void snd_pcm_set_state(struct snd_pcm_substream *substream, int state)
+{
+	snd_pcm_stream_lock_irq(substream);
+	if (substream->runtime->status->state != SNDRV_PCM_STATE_DISCONNECTED)
+		substream->runtime->status->state = state;
+	snd_pcm_stream_unlock_irq(substream);
+}
+
 static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
 			     struct snd_pcm_hw_params *params)
 {
@@ -452,7 +460,7 @@ static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
 		runtime->boundary *= 2;
 
 	snd_pcm_timer_resolution_change(substream);
-	runtime->status->state = SNDRV_PCM_STATE_SETUP;
+	snd_pcm_set_state(substream, SNDRV_PCM_STATE_SETUP);
 
 	if (pm_qos_request_active(&substream->latency_pm_qos_req))
 		pm_qos_remove_request(&substream->latency_pm_qos_req);
@@ -464,7 +472,7 @@ static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
 	/* hardware might be unusable from this time,
 	   so we force application to retry to set
 	   the correct hardware parameter settings */
-	runtime->status->state = SNDRV_PCM_STATE_OPEN;
+	snd_pcm_set_state(substream, SNDRV_PCM_STATE_OPEN);
 	if (substream->ops->hw_free != NULL)
 		substream->ops->hw_free(substream);
 	return err;
@@ -512,7 +520,7 @@ static int snd_pcm_hw_free(struct snd_pcm_substream *substream)
 		return -EBADFD;
 	if (substream->ops->hw_free)
 		result = substream->ops->hw_free(substream);
-	runtime->status->state = SNDRV_PCM_STATE_OPEN;
+	snd_pcm_set_state(substream, SNDRV_PCM_STATE_OPEN);
 	pm_qos_remove_request(&substream->latency_pm_qos_req);
 	return result;
 }
@@ -1320,7 +1328,7 @@ static void snd_pcm_post_prepare(struct snd_pcm_substream *substream, int state)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	runtime->control->appl_ptr = runtime->status->hw_ptr;
-	runtime->status->state = SNDRV_PCM_STATE_PREPARED;
+	snd_pcm_set_state(substream, SNDRV_PCM_STATE_PREPARED);
 }
 
 static struct action_ops snd_pcm_action_prepare = {
-- 
1.7.12.3