[PATCH 4.6 41/81] gpiolib: Fix unaligned used of reference counters

Greg Kroah-Hartman
2016-06-22T23:01:08Z

From: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>

commit f4833b8cc7edab57d3f3033e549111a546c2e02b upstream.

gpiolib relies on the reference counters to clean up the gpio_device
structure.

Although the number of get/put is properly aligned on gpiolib.c
itself, it does not take into consideration how the referece counters
are affected by other external functions such as cdev_add and device_add.

Because of this, after the last call to put_device, the reference counter
has a value of +3, therefore never calling gpiodevice_release.

Due to the fact that some of the device has already been cleaned on
gpiochip_remove, the library will end up OOPsing the kernel (e.g. a call
to of_gpiochip_find_and_xlate).

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpio/gpiolib.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -438,7 +438,6 @@ static void gpiodevice_release(struct de
{
struct gpio_device *gdev = dev_get_drvdata(dev);

- cdev_del(&gdev->chrdev);
list_del(&gdev->list);
ida_simple_remove(&gpio_ida, gdev->id);
kfree(gdev->label);
@@ -471,7 +470,6 @@ static int gpiochip_setup_dev(struct gpi

/* From this point, the .release() function cleans up gpio_device */
gdev->dev.release = gpiodevice_release;
- get_device(&gdev->dev);
pr_debug("%s: registered GPIOs %d to %d on device: %s (%s)\n",
__func__, gdev->base, gdev->base + gdev->ngpio - 1,
dev_name(&gdev->dev), gdev->chip->label ? : "generic");
@@ -742,6 +740,8 @@ void gpiochip_remove(struct gpio_chip *c
* be removed, else it will be dangling until the last user is
* gone.
*/
+ cdev_del(&gdev->chrdev);
+ device_del(&gdev->dev);
put_device(&gdev->dev);
}
EXPORT_SYMBOL_GPL(gpiochip_remove);