[PATCH] driver core: faux: stop using static struct device

[PATCH] driver core: faux: stop using static struct device

[Greg Kroah-Hartman]

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@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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;
 
-	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;
 }
-- 
2.52.0

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

[Danilo Krummrich]

On Wed Jan 21, 2026 at 11:29 AM CET, Greg Kroah-Hartman 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@gmail.com>

Closes: https://lore.kernel.org/lkml/CALbr=LYKJsj6cbrDLA07qioKhWJcRj+gW8=bq5=4ZvpEe2c4Yg@mail.gmail.com/

> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Reviewed-by: Danilo Krummrich <dakr@kernel.org>

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

[David Laight]

On Wed, 21 Jan 2026 11:29:45 +0100
Greg Kroah-Hartman <gregkh@linuxfoundation.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@gmail.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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;
>  }

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

[Greg Kroah-Hartman]

On Wed, Jan 21, 2026 at 02:55:24PM +0000, David Laight wrote:
> On Wed, 21 Jan 2026 11:29:45 +0100
> Greg Kroah-Hartman <gregkh@linuxfoundation.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@gmail.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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?

How can that happen?

> While I guess there shouldn't be two of these, better be safe.

It can't, no need for that :)

thanks,

greg k-h