staging: comedi: restrict comedi_set_hw_dev() usage

Don't allow comedi drivers to change `dev->hw_dev` using
`comedi_set_hw_dev()` if it's already been set.  Return `-EEXIST` in
that case.

`dev->hw_dev` needs to be set to NULL by the core during clean-up of the
comedi device, so add a local function `comedi_clear_hw_dev()` to do
that.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers.c b/drivers/staging/comedi/drivers.c
index 5adf9fc45de464bfebae22bc79bd12ce0406a256..d91b173b1f407b3d919080407f6185dccaadbf74 100644 (file)
--- a/drivers/staging/comedi/drivers.c
+++ b/drivers/staging/comedi/drivers.c
@@ -45,14 +45,21 @@ struct comedi_driver *comedi_drivers;
 
 int comedi_set_hw_dev(struct comedi_device *dev, struct device *hw_dev)
 {
-       struct device *old_hw_dev = dev->hw_dev;
-
+       if (hw_dev == dev->hw_dev)
+               return 0;
+       if (dev->hw_dev != NULL)
+               return -EEXIST;
        dev->hw_dev = get_device(hw_dev);
-       put_device(old_hw_dev);
        return 0;
 }
 EXPORT_SYMBOL_GPL(comedi_set_hw_dev);
 
+static void comedi_clear_hw_dev(struct comedi_device *dev)
+{
+       put_device(dev->hw_dev);
+       dev->hw_dev = NULL;
+}
+
 int comedi_alloc_subdevices(struct comedi_device *dev, int num_subdevices)
 {
        struct comedi_subdevice *s;
@@ -108,7 +115,7 @@ static void cleanup_device(struct comedi_device *dev)
        dev->write_subdev = NULL;
        dev->open = NULL;
        dev->close = NULL;
-       comedi_set_hw_dev(dev, NULL);
+       comedi_clear_hw_dev(dev);
 }
 
 static void __comedi_device_detach(struct comedi_device *dev)