Patch "ALSA: usb-audio: scarlett2: Fix data_mutex lock" has been added to the 5.13-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ALSA: usb-audio: scarlett2: Fix data_mutex lock

to the 5.13-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     alsa-usb-audio-scarlett2-fix-data_mutex-lock.patch
and it can be found in the queue-5.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit d85e475b1a3ca97c82f5384da1e42533818577b8
Author: Geoffrey D. Bennett <g@xxxxx>
Date:   Mon Jun 21 02:16:43 2021 +0930

    ALSA: usb-audio: scarlett2: Fix data_mutex lock
    
    [ Upstream commit 9b5ddea9ce5a68d7d2bedcb69901ac2a86c96c7b ]
    
    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@xxxxx>
    Link: https://lore.kernel.org/r/20210620164643.GA9216@xxxxxxx
    Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c
index 1982e67a0f32..2ea41c8eafd1 100644
--- a/sound/usb/mixer_scarlett_gen2.c
+++ b/sound/usb/mixer_scarlett_gen2.c
@@ -1033,11 +1033,10 @@ static int scarlett2_master_volume_ctl_get(struct snd_kcontrol *kctl,
 	struct usb_mixer_interface *mixer = elem->head.mixer;
 	struct scarlett2_mixer_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;
@@ -1051,11 +1050,10 @@ static int scarlett2_volume_ctl_get(struct snd_kcontrol *kctl,
 	struct scarlett2_mixer_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;
@@ -1319,11 +1317,10 @@ static int scarlett2_button_ctl_get(struct snd_kcontrol *kctl,
 	struct usb_mixer_interface *mixer = elem->head.mixer;
 	struct scarlett2_mixer_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;