linux-kernel - Re: [PATCH 01/22] virtio: store owner from modules with register_virtio

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Date: Fri, 29 Mar 2024 12:42:08 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: "Michael S. Tsirkin" <mst@...hat.com>, 
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Subject: Re: [PATCH 01/22] virtio: store owner from modules with
 register_virtio_driver()

On Wed, Mar 27, 2024 at 01:40:54PM +0100, Krzysztof Kozlowski wrote:
>Modules registering driver with register_virtio_driver() might forget to
>set .owner field.  i2c-virtio.c for example has it missing.  The field
>is used by some of other kernel parts for reference counting
>(try_module_get()), so it is expected that drivers will set it.
>
>Solve the problem by moving this task away from the drivers to the core
>amba bus code, just like we did for platform_driver in
>commit 9447057eaff8 ("platform_device: use a macro instead of
>platform_driver_register").
>
>Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>---
> Documentation/driver-api/virtio/writing_virtio_drivers.rst | 1 -
> drivers/virtio/virtio.c                                    | 6 ++++--
> include/linux/virtio.h                                     | 7 +++++--
> 3 files changed, 9 insertions(+), 5 deletions(-)
>
>diff --git a/Documentation/driver-api/virtio/writing_virtio_drivers.rst b/Documentation/driver-api/virtio/writing_virtio_drivers.rst
>index e14c58796d25..e5de6f5d061a 100644
>--- a/Documentation/driver-api/virtio/writing_virtio_drivers.rst
>+++ b/Documentation/driver-api/virtio/writing_virtio_drivers.rst
>@@ -97,7 +97,6 @@ like this::
>
> 	static struct virtio_driver virtio_dummy_driver = {
> 		.driver.name =  KBUILD_MODNAME,
>-		.driver.owner = THIS_MODULE,
> 		.id_table =     id_table,
> 		.probe =        virtio_dummy_probe,
> 		.remove =       virtio_dummy_remove,
>diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
>index f173587893cb..9510c551dce8 100644
>--- a/drivers/virtio/virtio.c
>+++ b/drivers/virtio/virtio.c
>@@ -362,14 +362,16 @@ static const struct bus_type virtio_bus = {
> 	.remove = virtio_dev_remove,
> };
>
>-int register_virtio_driver(struct virtio_driver *driver)
>+int __register_virtio_driver(struct virtio_driver *driver, struct module *owner)
> {
> 	/* Catch this early. */
> 	BUG_ON(driver->feature_table_size && !driver->feature_table);
> 	driver->driver.bus = &virtio_bus;
>+	driver->driver.owner = owner;
>+

`.driver.name =  KBUILD_MODNAME` also seems very common, should we put
that in the macro as well?

> 	return driver_register(&driver->driver);
> }
>-EXPORT_SYMBOL_GPL(register_virtio_driver);
>+EXPORT_SYMBOL_GPL(__register_virtio_driver);
>
> void unregister_virtio_driver(struct virtio_driver *driver)
> {
>diff --git a/include/linux/virtio.h b/include/linux/virtio.h
>index b0201747a263..26c4325aa373 100644
>--- a/include/linux/virtio.h
>+++ b/include/linux/virtio.h
>@@ -170,7 +170,7 @@ size_t virtio_max_dma_size(const struct virtio_device *vdev);
>
> /**
>  * struct virtio_driver - operations for a virtio I/O driver
>- * @driver: underlying device driver (populate name and owner).
>+ * @driver: underlying device driver (populate name).
>  * @id_table: the ids serviced by this driver.
>  * @feature_table: an array of feature numbers supported by this driver.
>  * @feature_table_size: number of entries in the feature table array.
>@@ -208,7 +208,10 @@ static inline struct virtio_driver *drv_to_virtio(struct device_driver *drv)
> 	return container_of(drv, struct virtio_driver, driver);
> }
>
>-int register_virtio_driver(struct virtio_driver *drv);
>+/* use a macro to avoid include chaining to get THIS_MODULE */
>+#define register_virtio_driver(drv) \
>+	__register_virtio_driver(drv, THIS_MODULE)
>+int __register_virtio_driver(struct virtio_driver *drv, struct module *owner);
> void unregister_virtio_driver(struct virtio_driver *drv);
>
> /* module_virtio_driver() - Helper macro for drivers that don't do
>
>-- 
>2.34.1
>