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

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Message-Id: <20160622223745.363905915@linuxfoundation.org>
Date:	Wed, 22 Jun 2016 15:46:04 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: [PATCH 4.6 41/81] gpiolib: Fix unaligned used of reference counters

4.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ricardo Ribalda Delgado <ricardo.ribalda@...il.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@...il.com>
Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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);