[PATCH] software node: replace -EEXIST with -EBUSY

[Daniel Gomez <da.gomez@kernel.org>]

From: Daniel Gomez <da.gomez@samsung.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@samsung.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.

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;

---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20251219-dev-module-init-eexists-linux-acpi-110964d37acd

Best regards,
--  
Daniel Gomez <da.gomez@samsung.com>