diff --git a/drivers/staging/comedi/kcomedilib/kcomedilib_main.c b/drivers/staging/comedi/kcomedilib/kcomedilib_main.c
index b3a06f2dbad6e142ae25f567c57707b2febd7b85..7dc5a18e69d42bd4bd8e9df3d2458d368f769753 100644
--- a/drivers/staging/comedi/kcomedilib/kcomedilib_main.c
+++ b/drivers/staging/comedi/kcomedilib/kcomedilib_main.c
@@ -50,10 +50,12 @@ struct comedi_device *comedi_open(const char *filename)
 	if (!dev)
 		return NULL;
 
-	if (dev->attached && try_module_get(dev->driver->module))
+	down_read(&dev->attach_lock);
+	if (dev->attached)
 		retval = dev;
 	else
 		retval = NULL;
+	up_read(&dev->attach_lock);
 
 	if (retval == NULL)
 		comedi_dev_put(dev);
@@ -62,13 +64,9 @@ struct comedi_device *comedi_open(const char *filename)
 }
 EXPORT_SYMBOL_GPL(comedi_open);
 
-int comedi_close(struct comedi_device *d)
+int comedi_close(struct comedi_device *dev)
 {
-	struct comedi_device *dev = (struct comedi_device *)d;
-
-	module_put(dev->driver->module);
 	comedi_dev_put(dev);
-
 	return 0;
 }
 EXPORT_SYMBOL_GPL(comedi_close);
@@ -78,7 +76,14 @@ static int comedi_do_insn(struct comedi_device *dev,
 			  unsigned int *data)
 {
 	struct comedi_subdevice *s;
-	int ret = 0;
+	int ret;
+
+	mutex_lock(&dev->mutex);
+
+	if (!dev->attached) {
+		ret = -EINVAL;
+		goto error;
+	}
 
 	/* a subdevice instruction */
 	if (insn->subdev >= dev->n_subdevices) {
@@ -125,6 +130,7 @@ static int comedi_do_insn(struct comedi_device *dev,
 	s->busy = NULL;
 error:
 
+	mutex_unlock(&dev->mutex);
 	return ret;
 }
 
@@ -174,9 +180,6 @@ int comedi_dio_bitfield2(struct comedi_device *dev, unsigned int subdev,
 	unsigned int shift;
 	int ret;
 
-	if (subdev >= dev->n_subdevices)
-		return -EINVAL;
-
 	base_channel = CR_CHAN(base_channel);
 	n_chan = comedi_get_n_channels(dev, subdev);
 	if (base_channel >= n_chan)
@@ -216,23 +219,33 @@ int comedi_find_subdevice_by_type(struct comedi_device *dev, int type,
 				  unsigned int subd)
 {
 	struct comedi_subdevice *s;
-
-	if (subd > dev->n_subdevices)
-		return -ENODEV;
-
-	for (; subd < dev->n_subdevices; subd++) {
-		s = &dev->subdevices[subd];
-		if (s->type == type)
-			return subd;
-	}
-	return -1;
+	int ret = -ENODEV;
+
+	down_read(&dev->attach_lock);
+	if (dev->attached)
+		for (; subd < dev->n_subdevices; subd++) {
+			s = &dev->subdevices[subd];
+			if (s->type == type) {
+				ret = subd;
+				break;
+			}
+		}
+	up_read(&dev->attach_lock);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(comedi_find_subdevice_by_type);
 
 int comedi_get_n_channels(struct comedi_device *dev, unsigned int subdevice)
 {
-	struct comedi_subdevice *s = &dev->subdevices[subdevice];
+	int n;
+
+	down_read(&dev->attach_lock);
+	if (!dev->attached || subdevice >= dev->n_subdevices)
+		n = 0;
+	else
+		n = dev->subdevices[subdevice].n_chan;
+	up_read(&dev->attach_lock);
 
-	return s->n_chan;
+	return n;
 }
 EXPORT_SYMBOL_GPL(comedi_get_n_channels);