diff --git a/drivers/comedi/drivers/comedi_test.c b/drivers/comedi/drivers/comedi_test.c
index 30ea8b53ebf8..05ae9122823f 100644
--- a/drivers/comedi/drivers/comedi_test.c
+++ b/drivers/comedi/drivers/comedi_test.c
@@ -87,6 +87,8 @@ struct waveform_private {
 	struct comedi_device *dev;	/* parent comedi device */
 	u64 ao_last_scan_time;		/* time of previous AO scan in usec */
 	unsigned int ao_scan_period;	/* AO scan period in usec */
+	bool ai_timer_enable:1;		/* should AI timer be running? */
+	bool ao_timer_enable:1;		/* should AO timer be running? */
 	unsigned short ao_loopbacks[N_CHANS];
 };
 
@@ -236,8 +238,12 @@ static void waveform_ai_timer(struct timer_list *t)
 			time_increment = devpriv->ai_convert_time - now;
 		else
 			time_increment = 1;
-		mod_timer(&devpriv->ai_timer,
-			  jiffies + usecs_to_jiffies(time_increment));
+		spin_lock(&dev->spinlock);
+		if (devpriv->ai_timer_enable) {
+			mod_timer(&devpriv->ai_timer,
+				  jiffies + usecs_to_jiffies(time_increment));
+		}
+		spin_unlock(&dev->spinlock);
 	}
 
 overrun:
@@ -393,9 +399,12 @@ static int waveform_ai_cmd(struct comedi_device *dev,
 	 * Seem to need an extra jiffy here, otherwise timer expires slightly
 	 * early!
 	 */
+	spin_lock_bh(&dev->spinlock);
+	devpriv->ai_timer_enable = true;
 	devpriv->ai_timer.expires =
 		jiffies + usecs_to_jiffies(devpriv->ai_convert_period) + 1;
 	add_timer(&devpriv->ai_timer);
+	spin_unlock_bh(&dev->spinlock);
 	return 0;
 }
 
@@ -404,6 +413,9 @@ static int waveform_ai_cancel(struct comedi_device *dev,
 {
 	struct waveform_private *devpriv = dev->private;
 
+	spin_lock_bh(&dev->spinlock);
+	devpriv->ai_timer_enable = false;
+	spin_unlock_bh(&dev->spinlock);
 	if (in_softirq()) {
 		/* Assume we were called from the timer routine itself. */
 		del_timer(&devpriv->ai_timer);
@@ -495,8 +507,12 @@ static void waveform_ao_timer(struct timer_list *t)
 		unsigned int time_inc = devpriv->ao_last_scan_time +
 					devpriv->ao_scan_period - now;
 
-		mod_timer(&devpriv->ao_timer,
-			  jiffies + usecs_to_jiffies(time_inc));
+		spin_lock(&dev->spinlock);
+		if (devpriv->ao_timer_enable) {
+			mod_timer(&devpriv->ao_timer,
+				  jiffies + usecs_to_jiffies(time_inc));
+		}
+		spin_unlock(&dev->spinlock);
 	}
 
 underrun:
@@ -517,9 +533,12 @@ static int waveform_ao_inttrig_start(struct comedi_device *dev,
 	async->inttrig = NULL;
 
 	devpriv->ao_last_scan_time = ktime_to_us(ktime_get());
+	spin_lock_bh(&dev->spinlock);
+	devpriv->ao_timer_enable = true;
 	devpriv->ao_timer.expires =
 		jiffies + usecs_to_jiffies(devpriv->ao_scan_period);
 	add_timer(&devpriv->ao_timer);
+	spin_unlock_bh(&dev->spinlock);
 
 	return 1;
 }
@@ -604,6 +623,9 @@ static int waveform_ao_cancel(struct comedi_device *dev,
 	struct waveform_private *devpriv = dev->private;
 
 	s->async->inttrig = NULL;
+	spin_lock_bh(&dev->spinlock);
+	devpriv->ao_timer_enable = false;
+	spin_unlock_bh(&dev->spinlock);
 	if (in_softirq()) {
 		/* Assume we were called from the timer routine itself. */
 		del_timer(&devpriv->ao_timer);