gpio: fix gpio-device list corruption

commit cf25ef6 upstream.

Make sure to hold the gpio_lock when removing the gpio device from the
gpio_devices list (when dropping the last reference) to avoid corrupting
the list when there are concurrent accesses.

Fixes: ff2b135 ("gpio: make the gpiochip a real device")
Cc: stable@vger.kernel.org      # 4.6
Reviewed-by: Saravana Kannan <saravanak@google.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
[ johan: adjust context to 5.11 ]
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpio/gpiolib.c

@@ -472,8 +472,12 @@ EXPORT_SYMBOL_GPL(gpiochip_line_is_valid);
 static void gpiodevice_release(struct device *dev)
 {
 	struct gpio_device *gdev = dev_get_drvdata(dev);
+	unsigned long flags;
 
+	spin_lock_irqsave(&gpio_lock, flags);
 	list_del(&gdev->list);
+	spin_unlock_irqrestore(&gpio_lock, flags);
+
 	ida_free(&gpio_ida, gdev->id);
 	kfree_const(gdev->label);
 	kfree(gdev->descs);