[8/8] ALSA: usb-audio: scarlett2: Fix data_mutex lock

Commit Message

Geoffrey D. Bennett June 6, 2021, 5:47 p.m. UTC

The private->vol_updated flag was being checked outside of the
mutex_lock/unlock() of private->data_mutex leading to the volume data
being fetched twice from the device unnecessarily or old volume data
being returned.

Update scarlett2_*_ctl_get() and include the private->vol_updated flag
check inside the critical region.

Signed-off-by: Geoffrey D. Bennett <[e-mail]>
---
 sound/usb/mixer_scarlett_gen2.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

Patch

diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c
index 8a4aa16cc364..9ea6abded26e 100644
--- a/sound/usb/mixer_scarlett_gen2.c
+++ b/sound/usb/mixer_scarlett_gen2.c
@@ -1155,11 +1155,10 @@  static int scarlett2_master_volume_ctl_get(struct snd_kcontrol *kctl,
 	struct usb_mixer_interface *mixer = elem->head.mixer;
 	struct scarlett2_data *private = mixer->private_data;
 
-	if (private->vol_updated) {
-		mutex_lock(&private->data_mutex);
+	mutex_lock(&private->data_mutex);
+	if (private->vol_updated)
 		scarlett2_update_volumes(mixer);
-		mutex_unlock(&private->data_mutex);
-	}
+	mutex_unlock(&private->data_mutex);
 
 	ucontrol->value.integer.value[0] = private->master_vol;
 	return 0;
@@ -1173,11 +1172,10 @@  static int scarlett2_volume_ctl_get(struct snd_kcontrol *kctl,
 	struct scarlett2_data *private = mixer->private_data;
 	int index = elem->control;
 
-	if (private->vol_updated) {
-		mutex_lock(&private->data_mutex);
+	mutex_lock(&private->data_mutex);
+	if (private->vol_updated)
 		scarlett2_update_volumes(mixer);
-		mutex_unlock(&private->data_mutex);
-	}
+	mutex_unlock(&private->data_mutex);
 
 	ucontrol->value.integer.value[0] = private->vol[index];
 	return 0;
@@ -1441,11 +1439,10 @@  static int scarlett2_button_ctl_get(struct snd_kcontrol *kctl,
 	struct usb_mixer_interface *mixer = elem->head.mixer;
 	struct scarlett2_data *private = mixer->private_data;
 
-	if (private->vol_updated) {
-		mutex_lock(&private->data_mutex);
+	mutex_lock(&private->data_mutex);
+	if (private->vol_updated)
 		scarlett2_update_volumes(mixer);
-		mutex_unlock(&private->data_mutex);
-	}
+	mutex_unlock(&private->data_mutex);
 
 	ucontrol->value.enumerated.item[0] = private->buttons[elem->control];
 	return 0;