ALSA: snd-usb-caiaq: Missing lock around use of buffer positions

Fix a race which causes snd_pcm_update_hw_ptr_pos() to report a bug.
Signed-off-by: Mark Hills <mark@pogo.org.uk>
Acked-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/caiaq/audio.c

@@ -269,16 +269,22 @@ snd_usb_caiaq_pcm_pointer(struct snd_pcm_substream *sub)
 {
 	int index = sub->number;
 	struct snd_usb_caiaqdev *dev = snd_pcm_substream_chip(sub);
+	snd_pcm_uframes_t ptr;
+
+	spin_lock(&dev->spinlock);
 
 	if (dev->input_panic || dev->output_panic)
-		return SNDRV_PCM_POS_XRUN;
+		ptr = SNDRV_PCM_POS_XRUN;
 
 	if (sub->stream == SNDRV_PCM_STREAM_PLAYBACK)
-		return bytes_to_frames(sub->runtime,
+		ptr = bytes_to_frames(sub->runtime,
 					dev->audio_out_buf_pos[index]);
 	else
-		return bytes_to_frames(sub->runtime,
+		ptr = bytes_to_frames(sub->runtime,
 					dev->audio_in_buf_pos[index]);
+
+	spin_unlock(&dev->spinlock);
+	return ptr;
 }
 
 /* operators for both playback and capture */