linux-kernel - Re: [PATCH] driver core: faux: stop using static struct device

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Message-ID: <20260121145524.2ecd29eb@pumpkin>
Date: Wed, 21 Jan 2026 14:55:24 +0000
From: David Laight <david.laight.linux@...il.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: dakr@...nel.org, rafael@...nel.org, linux-kernel@...r.kernel.org,
 driver-core@...ts.linux.dev, Gui-Dong Han <hanguidong02@...il.com>
Subject: Re: [PATCH] driver core: faux: stop using static struct device

On Wed, 21 Jan 2026 11:29:45 +0100
Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:

> faux_bus_root should not have been a static struct device, but rather a
> dynamically created structure so that lockdep and other testing tools do
> not trip over it (as well as being the right thing overall to do.)  Fix
> this up by making it properly dynamic.
> 
> Reported-by: Gui-Dong Han <hanguidong02@...il.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  drivers/base/faux.c | 18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/base/faux.c b/drivers/base/faux.c
> index 21dd02124231..23d725817232 100644
> --- a/drivers/base/faux.c
> +++ b/drivers/base/faux.c
> @@ -29,9 +29,7 @@ struct faux_object {
>  };
>  #define to_faux_object(dev) container_of_const(dev, struct faux_object, faux_dev.dev)
>  
> -static struct device faux_bus_root = {
> -	.init_name	= "faux",
> -};
> +static struct device *faux_bus_root;
>  
>  static int faux_match(struct device *dev, const struct device_driver *drv)
>  {
> @@ -152,7 +150,7 @@ struct faux_device *faux_device_create_with_groups(const char *name,
>  	if (parent)
>  		dev->parent = parent;
>  	else
> -		dev->parent = &faux_bus_root;
> +		dev->parent = faux_bus_root;
>  	dev->bus = &faux_bus_type;
>  	dev_set_name(dev, "%s", name);
>  	device_set_pm_not_required(dev);
> @@ -236,9 +234,15 @@ int __init faux_bus_init(void)
>  {
>  	int ret;

Should there be:
	if (faux_bus_root)
		return -EBUSY;
here?
While I guess there shouldn't be two of these, better be safe.

	David

>  
> -	ret = device_register(&faux_bus_root);
> +	faux_bus_root = kzalloc(sizeof(*faux_bus_root), GFP_KERNEL);
> +	if (!faux_bus_root)
> +		return -ENOMEM;
> +
> +	dev_set_name(faux_bus_root, "faux");
> +
> +	ret = device_register(faux_bus_root);
>  	if (ret) {
> -		put_device(&faux_bus_root);
> +		put_device(faux_bus_root);
>  		return ret;
>  	}
>  
> @@ -256,6 +260,6 @@ int __init faux_bus_init(void)
>  	bus_unregister(&faux_bus_type);
>  
>  error_bus:
> -	device_unregister(&faux_bus_root);
> +	device_unregister(faux_bus_root);
>  	return ret;
>  }