ALSA: usb-audio: scarlett2: Fix data_mutex lock

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 <g@b4.vu>
Link: https://lore.kernel.org/r/20210620164643.GA9216@m.b4.vu
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c
index cb8483d3c58a929bdec613c0618308576cefccaf..d6298ab1de561e36bcdbd21a6bed4aa0f465600a 100644 (file)
--- a/sound/usb/mixer_scarlett_gen2.c
+++ b/sound/usb/mixer_scarlett_gen2.c
@@ -1153,11 +1153,10 @@ 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;
@@ -1171,11 +1170,10 @@ 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;
@@ -1439,11 +1437,10 @@ static int scarlett2_dim_mute_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->dim_mute[elem->control];
        return 0;