[PATCH v2] virtio-mmio: fix device release warning on module unload

[Johan Hovold <johan@kernel.org>]

Driver core expects devices to be allocated dynamically and complains
loudly when a device that lacks a release function is freed.

Use __root_device_register() to allocate and register the root device
instead of open coding using a static device.

Note that root_device_register(), which also creates a link to the
module, cannot be used as the device is registered when parsing the
module parameters which happens before the module kobject has been set
up.

Fixes: 81a054ce0b46 ("virtio-mmio: Devices parameter parsing")
Cc: stable@vger.kernel.org	# 3.5
Cc: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
---

Changes in v2:
 - add sanity check to vm_cmdline_get() to prevent root from
   dereferencing an error pointer when reading back the module parameter
   through sysfs should root device registration ever fail when the
   driver is also built-in


 drivers/virtio/virtio_mmio.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 595c2274fbb5..510b7c4efdff 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -662,9 +662,7 @@ static void virtio_mmio_remove(struct platform_device *pdev)
 
 #if defined(CONFIG_VIRTIO_MMIO_CMDLINE_DEVICES)
 
-static struct device vm_cmdline_parent = {
-	.init_name = "virtio-mmio-cmdline",
-};
+static struct device *vm_cmdline_parent;
 
 static int vm_cmdline_parent_registered;
 static int vm_cmdline_id;
@@ -672,7 +670,6 @@ static int vm_cmdline_id;
 static int vm_cmdline_set(const char *device,
 		const struct kernel_param *kp)
 {
-	int err;
 	struct resource resources[2] = {};
 	char *str;
 	long long base, size;
@@ -704,11 +701,10 @@ static int vm_cmdline_set(const char *device,
 	resources[1].start = resources[1].end = irq;
 
 	if (!vm_cmdline_parent_registered) {
-		err = device_register(&vm_cmdline_parent);
-		if (err) {
-			put_device(&vm_cmdline_parent);
+		vm_cmdline_parent = __root_device_register("virtio-mmio-cmdline", NULL);
+		if (IS_ERR(vm_cmdline_parent)) {
 			pr_err("Failed to register parent device!\n");
-			return err;
+			return PTR_ERR(vm_cmdline_parent);
 		}
 		vm_cmdline_parent_registered = 1;
 	}
@@ -719,7 +715,7 @@ static int vm_cmdline_set(const char *device,
 		       (unsigned long long)resources[0].end,
 		       (int)resources[1].start);
 
-	pdev = platform_device_register_resndata(&vm_cmdline_parent,
+	pdev = platform_device_register_resndata(vm_cmdline_parent,
 			"virtio-mmio", vm_cmdline_id++,
 			resources, ARRAY_SIZE(resources), NULL, 0);
 
@@ -743,8 +739,12 @@ static int vm_cmdline_get_device(struct device *dev, void *data)
 static int vm_cmdline_get(char *buffer, const struct kernel_param *kp)
 {
 	buffer[0] = '\0';
-	device_for_each_child(&vm_cmdline_parent, buffer,
-			vm_cmdline_get_device);
+
+	if (vm_cmdline_parent_registered) {
+		device_for_each_child(vm_cmdline_parent, buffer,
+				vm_cmdline_get_device);
+	}
+
 	return strlen(buffer) + 1;
 }
 
@@ -766,9 +766,9 @@ static int vm_unregister_cmdline_device(struct device *dev,
 static void vm_unregister_cmdline_devices(void)
 {
 	if (vm_cmdline_parent_registered) {
-		device_for_each_child(&vm_cmdline_parent, NULL,
+		device_for_each_child(vm_cmdline_parent, NULL,
 				vm_unregister_cmdline_device);
-		device_unregister(&vm_cmdline_parent);
+		root_device_unregister(vm_cmdline_parent);
 		vm_cmdline_parent_registered = 0;
 	}
 }
-- 
2.53.0