3 files changed, 35 insertions, 10 deletions

diff --git a/drivers/comedi/comedi_fops.c b/drivers/comedi/comedi_fops.c
index c83fd14dd7ad..23b7178522ae 100644
--- a/drivers/comedi/comedi_fops.c
+++ b/drivers/comedi/comedi_fops.c
@@ -787,6 +787,7 @@ static int is_device_busy(struct comedi_device *dev)
 	struct comedi_subdevice *s;
 	int i;
 
+	lockdep_assert_held_write(&dev->attach_lock);
 	lockdep_assert_held(&dev->mutex);
 	if (!dev->attached)
 		return 0;
@@ -795,7 +796,16 @@ static int is_device_busy(struct comedi_device *dev)
 		s = &dev->subdevices[i];
 		if (s->busy)
 			return 1;
-		if (s->async && comedi_buf_is_mmapped(s))
+		if (!s->async)
+			continue;
+		if (comedi_buf_is_mmapped(s))
+			return 1;
+		/*
+		 * There may be tasks still waiting on the subdevice's wait
+		 * queue, although they should already be about to be removed
+		 * from it since the subdevice has no active async command.
+		 */
+		if (wq_has_sleeper(&s->async->wait_head))
 			return 1;
 	}
 
@@ -825,15 +835,22 @@ static int do_devconfig_ioctl(struct comedi_device *dev,
 		return -EPERM;
 
 	if (!arg) {
-		if (is_device_busy(dev))
-			return -EBUSY;
+		int rc = 0;
+
 		if (dev->attached) {
-			struct module *driver_module = dev->driver->module;
+			down_write(&dev->attach_lock);
+			if (is_device_busy(dev)) {
+				rc = -EBUSY;
+			} else {
+				struct module *driver_module =
+					dev->driver->module;
 
-			comedi_device_detach(dev);
-			module_put(driver_module);
+				comedi_device_detach_locked(dev);
+				module_put(driver_module);
+			}
+			up_write(&dev->attach_lock);
 		}
-		return 0;
+		return rc;
 	}
 
 	if (copy_from_user(&it, arg, sizeof(it)))
diff --git a/drivers/comedi/comedi_internal.h b/drivers/comedi/comedi_internal.h
index 9b3631a654c8..cf10ba016ebc 100644
--- a/drivers/comedi/comedi_internal.h
+++ b/drivers/comedi/comedi_internal.h
@@ -50,6 +50,7 @@ extern struct mutex comedi_drivers_list_lock;
 int insn_inval(struct comedi_device *dev, struct comedi_subdevice *s,
 	       struct comedi_insn *insn, unsigned int *data);
 
+void comedi_device_detach_locked(struct comedi_device *dev);
 void comedi_device_detach(struct comedi_device *dev);
 int comedi_device_attach(struct comedi_device *dev,
 			 struct comedi_devconfig *it);
diff --git a/drivers/comedi/drivers.c b/drivers/comedi/drivers.c
index 9e4b7c840a8f..f1dc854928c1 100644
--- a/drivers/comedi/drivers.c
+++ b/drivers/comedi/drivers.c
@@ -158,7 +158,7 @@ static void comedi_device_detach_cleanup(struct comedi_device *dev)
 	int i;
 	struct comedi_subdevice *s;
 
-	lockdep_assert_held(&dev->attach_lock);
+	lockdep_assert_held_write(&dev->attach_lock);
 	lockdep_assert_held(&dev->mutex);
 	if (dev->subdevices) {
 		for (i = 0; i < dev->n_subdevices; i++) {
@@ -196,16 +196,23 @@ static void comedi_device_detach_cleanup(struct comedi_device *dev)
 	comedi_clear_hw_dev(dev);
 }
 
-void comedi_device_detach(struct comedi_device *dev)
+void comedi_device_detach_locked(struct comedi_device *dev)
 {
+	lockdep_assert_held_write(&dev->attach_lock);
 	lockdep_assert_held(&dev->mutex);
 	comedi_device_cancel_all(dev);
-	down_write(&dev->attach_lock);
 	dev->attached = false;
 	dev->detach_count++;
 	if (dev->driver)
 		dev->driver->detach(dev);
 	comedi_device_detach_cleanup(dev);
+}
+
+void comedi_device_detach(struct comedi_device *dev)
+{
+	lockdep_assert_held(&dev->mutex);
+	down_write(&dev->attach_lock);
+	comedi_device_detach_locked(dev);
 	up_write(&dev->attach_lock);
 }