ALSA: pcm - Fix race with proc files

The PCM proc files may open a race against substream close, which can
end up with an Oops.  Use the open_mutex to protect for it.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm.c

@@ -372,14 +372,17 @@ static void snd_pcm_substream_proc_hw_params_read(struct snd_info_entry *entry,
 						  struct snd_info_buffer *buffer)
 {
 	struct snd_pcm_substream *substream = entry->private_data;
-	struct snd_pcm_runtime *runtime = substream->runtime;
+	struct snd_pcm_runtime *runtime;
+
+	mutex_lock(&substream->pcm->open_mutex);
+	runtime = substream->runtime;
 	if (!runtime) {
 		snd_iprintf(buffer, "closed\n");
-		return;
+		goto unlock;
 	}
 	if (runtime->status->state == SNDRV_PCM_STATE_OPEN) {
 		snd_iprintf(buffer, "no setup\n");
-		return;
+		goto unlock;
 	}
 	snd_iprintf(buffer, "access: %s\n", snd_pcm_access_name(runtime->access));
 	snd_iprintf(buffer, "format: %s\n", snd_pcm_format_name(runtime->format));
@@ -398,20 +401,25 @@ static void snd_pcm_substream_proc_hw_params_read(struct snd_info_entry *entry,
 		snd_iprintf(buffer, "OSS period frames: %lu\n", (unsigned long)runtime->oss.period_frames);
 	}
 #endif
+ unlock:
+	mutex_unlock(&substream->pcm->open_mutex);
 }
 
 static void snd_pcm_substream_proc_sw_params_read(struct snd_info_entry *entry,
 						  struct snd_info_buffer *buffer)
 {
 	struct snd_pcm_substream *substream = entry->private_data;
-	struct snd_pcm_runtime *runtime = substream->runtime;
+	struct snd_pcm_runtime *runtime;
+
+	mutex_lock(&substream->pcm->open_mutex);
+	runtime = substream->runtime;
 	if (!runtime) {
 		snd_iprintf(buffer, "closed\n");
-		return;
+		goto unlock;
 	}
 	if (runtime->status->state == SNDRV_PCM_STATE_OPEN) {
 		snd_iprintf(buffer, "no setup\n");
-		return;
+		goto unlock;
 	}
 	snd_iprintf(buffer, "tstamp_mode: %s\n", snd_pcm_tstamp_mode_name(runtime->tstamp_mode));
 	snd_iprintf(buffer, "period_step: %u\n", runtime->period_step);
@@ -421,24 +429,29 @@ static void snd_pcm_substream_proc_sw_params_read(struct snd_info_entry *entry,
 	snd_iprintf(buffer, "silence_threshold: %lu\n", runtime->silence_threshold);
 	snd_iprintf(buffer, "silence_size: %lu\n", runtime->silence_size);
 	snd_iprintf(buffer, "boundary: %lu\n", runtime->boundary);
+ unlock:
+	mutex_unlock(&substream->pcm->open_mutex);
 }
 
 static void snd_pcm_substream_proc_status_read(struct snd_info_entry *entry,
 					       struct snd_info_buffer *buffer)
 {
 	struct snd_pcm_substream *substream = entry->private_data;
-	struct snd_pcm_runtime *runtime = substream->runtime;
+	struct snd_pcm_runtime *runtime;
 	struct snd_pcm_status status;
 	int err;
+
+	mutex_lock(&substream->pcm->open_mutex);
+	runtime = substream->runtime;
 	if (!runtime) {
 		snd_iprintf(buffer, "closed\n");
-		return;
+		goto unlock;
 	}
 	memset(&status, 0, sizeof(status));
 	err = snd_pcm_status(substream, &status);
 	if (err < 0) {
 		snd_iprintf(buffer, "error %d\n", err);
-		return;
+		goto unlock;
 	}
 	snd_iprintf(buffer, "state: %s\n", snd_pcm_state_name(status.state));
 	snd_iprintf(buffer, "owner_pid   : %d\n", pid_vnr(substream->pid));
@@ -452,6 +465,8 @@ static void snd_pcm_substream_proc_status_read(struct snd_info_entry *entry,
 	snd_iprintf(buffer, "-----\n");
 	snd_iprintf(buffer, "hw_ptr      : %ld\n", runtime->status->hw_ptr);
 	snd_iprintf(buffer, "appl_ptr    : %ld\n", runtime->control->appl_ptr);
+ unlock:
+	mutex_unlock(&substream->pcm->open_mutex);
 }
 
 #ifdef CONFIG_SND_PCM_XRUN_DEBUG