linux-kernel - Re: [PATCH] software node: replace -EEXIST with -EBUSY

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Message-ID: <aUht13bTn-lEnNM-@kekkonen.localdomain>
Date: Sun, 21 Dec 2025 23:59:51 +0200
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Daniel Gomez <da.gomez@...nel.org>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Daniel Scally <djrscally@...il.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Aaron Tomlin <atomlin@...mlin.com>,
	Lucas De Marchi <demarchi@...nel.org>, linux-acpi@...r.kernel.org,
	linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org,
	Daniel Gomez <da.gomez@...sung.com>
Subject: Re: [PATCH] software node: replace -EEXIST with -EBUSY

Hi Daniel,

Thanks for the patch.

On Sat, Dec 20, 2025 at 04:55:00AM +0100, Daniel Gomez wrote:
> From: Daniel Gomez <da.gomez@...sung.com>
> 
> The -EEXIST error code is reserved by the module loading infrastructure
> to indicate that a module is already loaded. When a module's init
> function returns -EEXIST, userspace tools like kmod interpret this as
> "module already loaded" and treat the operation as successful, returning
> 0 to the user even though the module initialization actually failed.
> 
> This follows the precedent set by commit 54416fd76770 ("netfilter:
> conntrack: helper: Replace -EEXIST by -EBUSY") which fixed the same
> issue in nf_conntrack_helper_register().
> 
> Affected modules:
>   * meraki_mx100 pcengines_apuv2
> 
> Signed-off-by: Daniel Gomez <da.gomez@...sung.com>
> ---
> The error code -EEXIST is reserved by the kernel module loader to
> indicate that a module with the same name is already loaded. When a
> module's init function returns -EEXIST, kmod interprets this as "module
> already loaded" and reports success instead of failure [1].
> 
> The kernel module loader will include a safety net that provides -EEXIST
> to -EBUSY with a warning [2], and a documentation patch has been sent to
> prevent future occurrences [3].
> 
> These affected code paths were identified using a static analysis tool
> [4] that traces -EEXIST returns to module_init(). The tool was developed
> with AI assistance and all findings were manually validated.

This might not be the only case where -EEXIST may be returned by loading a
module. The patch is fine IMO but I'd just change -EEXIST to -EBUSY in e.g.
do_init_module() to avoid this being an actual bug elsewhere.

I wonder what others think.

> 
> Link: https://lore.kernel.org/all/aKEVQhJpRdiZSliu@orbyte.nwl.cc/ [1]
> Link: https://lore.kernel.org/all/20251013-module-warn-ret-v1-0-ab65b41af01f@intel.com/ [2]
> Link: https://lore.kernel.org/all/20251218-dev-module-init-eexists-modules-docs-v1-0-361569aa782a@samsung.com/ [3]
> Link: https://gitlab.com/-/snippets/4913469 [4]
> ---
>  drivers/base/swnode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
> index 16a8301c25d6..083593d99a18 100644
> --- a/drivers/base/swnode.c
> +++ b/drivers/base/swnode.c
> @@ -919,7 +919,7 @@ int software_node_register(const struct software_node *node)
>  	struct swnode *parent = software_node_to_swnode(node->parent);
>  
>  	if (software_node_to_swnode(node))
> -		return -EEXIST;
> +		return -EBUSY;
>  
>  	if (node->parent && !parent)
>  		return -EINVAL;
> 

-- 
Regards,

Sakari Ailus