ALSA: timer: Unconditionally unlink slave instances, too

Like the previous fix (commit c0317c0e87 "ALSA: timer: Fix
use-after-free problem"), we have to unlink slave timer instances
immediately at snd_timer_stop(), too.  Otherwise it may leave a stale
entry in the list if the slave instance is freed before actually
running.

Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20211105091517.21733-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/timer.c

@@ -665,23 +665,22 @@ static int snd_timer_stop1(struct snd_timer_instance *timeri, bool stop)
 static int snd_timer_stop_slave(struct snd_timer_instance *timeri, bool stop)
 {
 	unsigned long flags;
+	bool running;
 
 	spin_lock_irqsave(&slave_active_lock, flags);
-	if (!(timeri->flags & SNDRV_TIMER_IFLG_RUNNING)) {
-		spin_unlock_irqrestore(&slave_active_lock, flags);
-		return -EBUSY;
-	}
+	running = timeri->flags & SNDRV_TIMER_IFLG_RUNNING;
 	timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING;
 	if (timeri->timer) {
 		spin_lock(&timeri->timer->lock);
 		list_del_init(&timeri->ack_list);
 		list_del_init(&timeri->active_list);
-		snd_timer_notify1(timeri, stop ? SNDRV_TIMER_EVENT_STOP :
-				  SNDRV_TIMER_EVENT_PAUSE);
+		if (running)
+			snd_timer_notify1(timeri, stop ? SNDRV_TIMER_EVENT_STOP :
+					  SNDRV_TIMER_EVENT_PAUSE);
 		spin_unlock(&timeri->timer->lock);
 	}
 	spin_unlock_irqrestore(&slave_active_lock, flags);
-	return 0;
+	return running ? 0 : -EBUSY;
 }
 
 /*