linux-kernel - [PATCH AUTOSEL 5.12 086/104] ALSA: usb-audio: scarlett2: Fix data

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Date:   Fri,  9 Jul 2021 22:21:38 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     "Geoffrey D. Bennett" <g@...vu>, Takashi Iwai <tiwai@...e.de>,
        Sasha Levin <sashal@...nel.org>, alsa-devel@...a-project.org
Subject: [PATCH AUTOSEL 5.12 086/104] ALSA: usb-audio: scarlett2: Fix data_mutex lock

From: "Geoffrey D. Bennett" <g@...vu>

[ 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@...vu>
Link: https://lore.kernel.org/r/20210620164643.GA9216@m.b4.vu
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 sound/usb/mixer_scarlett_gen2.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c
index b2fa317ba2ab..63d6a5e45ba9 100644
--- a/sound/usb/mixer_scarlett_gen2.c
+++ b/sound/usb/mixer_scarlett_gen2.c
@@ -1028,11 +1028,10 @@ 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;
@@ -1046,11 +1045,10 @@ 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;
@@ -1314,11 +1312,10 @@ 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;
-- 
2.30.2