staging: comedi: simplify driver module counting

For a legacy device attachment with the `COMEDI_DEVCONFIG` ioctl,
`do_devconfig_ioctl()` calls `comedi_device_attach()` to find a matching
device driver and attach the device.  It then tries to increment the
device driver's module count and if that fails it detaches the device.
So on successful attachment of a device by the `COMEDI_DEVCONFIG` ioctl,
the device driver's module count will have been incremented.

`comedi_device_attach()` is called from nowhere else.  It already
increments the device driver's module count temporarily and decrements
it again; if it gets as far as calling `comedi_device_postconfig()` the
module count is decremented within that function.

Simplify the above by removing the decrement of the device driver module
count from `comedi_device_postconfig()`.  If the call to
`comedi_device_postconfig()` succeeds, `comedi_device_attach()` will
return with the module count still incremented, otherwise decrement the
module count before returning the error.  Don't try and increment the
module count in `do_devconfig_ioctl()` after a successful return from
`comedi_device_attach()` as the module count has now already been
incremented.

`comedi_device_postconfig()` is also called by `comedi_auto_config()`
which currently has to increment the device driver's module count
temporarily so that `comedi_device_postconfig()` can decrement it, but
always returns with no overall change to the module count.  Remove all
the module count manipulations from `comedi_device_postconfig()`.  There
is no other reason for `comedi_auto_config()` to increment the device
driver's module count temporarily, since it is only called (indirectly)
from the device driver itself (usually via one of the wrappers
`comedi_pci_auto_config()` or `comedi_usb_auto_config()`).

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 1c310e7..229be41 100644 (file)
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -520,7 +520,6 @@ static int do_devconfig_ioctl(struct comedi_device *dev,
                              struct comedi_devconfig __user *arg)
 {
        struct comedi_devconfig it;
-       int ret;
 
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;
@@ -551,15 +550,8 @@ static int do_devconfig_ioctl(struct comedi_device *dev,
                /* don't re-use dynamically allocated comedi devices */
                return -EBUSY;
 
-       ret = comedi_device_attach(dev, &it);
-       if (ret == 0) {
-               if (!try_module_get(dev->driver->module)) {
-                       comedi_device_detach(dev);
-                       ret = -ENOSYS;
-               }
-       }
-
-       return ret;
+       /* This increments the driver module count on success. */
+       return comedi_device_attach(dev, &it);
 }
 
 /*

diff --git a/drivers/staging/comedi/drivers.c b/drivers/staging/comedi/drivers.c
index caadd3b..73727a7 100644 (file)
--- a/drivers/staging/comedi/drivers.c
+++ b/drivers/staging/comedi/drivers.c
@@ -277,11 +277,11 @@ static int __comedi_device_postconfig(struct comedi_device *dev)
 }
 
 /* do a little post-config cleanup */
-/* called with module refcount incremented, decrements it */
 static int comedi_device_postconfig(struct comedi_device *dev)
 {
-       int ret = __comedi_device_postconfig(dev);
-       module_put(dev->driver->module);
+       int ret;
+
+       ret = __comedi_device_postconfig(dev);
        if (ret < 0) {
                __comedi_device_detach(dev);
                return ret;
@@ -400,7 +400,11 @@ int comedi_device_attach(struct comedi_device *dev, struct comedi_devconfig *it)
                __comedi_device_detach(dev);
                return ret;
        }
-       return comedi_device_postconfig(dev);
+       ret = comedi_device_postconfig(dev);
+       if (ret < 0)
+               module_put(dev->driver->module);
+       /* On success, the driver module count has been incremented. */
+       return ret;
 }
 
 int comedi_auto_config(struct device *hardware_device,
@@ -431,19 +435,13 @@ int comedi_auto_config(struct device *hardware_device,
                return PTR_ERR(comedi_dev);
        /* Note: comedi_alloc_board_minor() locked comedi_dev->mutex. */
 
-       if (!try_module_get(driver->module))
-               ret = -EIO;
-       else {
-               comedi_set_hw_dev(comedi_dev, hardware_device);
-               comedi_dev->driver = driver;
-               ret = driver->auto_attach(comedi_dev, context);
-               if (ret < 0) {
-                       module_put(driver->module);
-                       __comedi_device_detach(comedi_dev);
-               } else {
-                       ret = comedi_device_postconfig(comedi_dev);
-               }
-       }
+       comedi_set_hw_dev(comedi_dev, hardware_device);
+       comedi_dev->driver = driver;
+       ret = driver->auto_attach(comedi_dev, context);
+       if (ret < 0)
+               __comedi_device_detach(comedi_dev);
+       else
+               ret = comedi_device_postconfig(comedi_dev);
        mutex_unlock(&comedi_dev->mutex);
 
        if (ret < 0)