x86/amd_node: Fix PCI device reference counting in amd_smn_init()grafted

The local "root" pointer is a temporary variable used during the device
search. Therefore, refcount related to the search iterators should be cleaned
up after the search is complete.

Use the __free() cleanup macro to ensure the refcount is decremented when the
temporary pointer goes out of scope.

Additionally, increment the refcount when caching a root pointer. This ensures
the in-use refcount is separate from the temporary search refcounting.

Finally, drop the redundant "root = NULL" before the second search loop. The
pci_get_class() iterator always decrements the refcount of its "from"
argument, so the first loop can only fall through with "root" already NULL.

Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com
Reported-by: Sashiko <sashiko-bot@kernel.org>
Assisted-by: LLM
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com

1 files changed, 114 insertions, 0 deletions

diff --git a/drivers/base/module.c b/drivers/base/module.c
new file mode 100644
index 000000000..6789dca48
--- /dev/null
+++ b/drivers/base/module.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * module.c - module sysfs fun for drivers
+ */
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include "base.h"
+
+static char *make_driver_name(const struct device_driver *drv)
+{
+	char *driver_name;
+
+	driver_name = kasprintf(GFP_KERNEL, "%s:%s", drv->bus->name, drv->name);
+	if (!driver_name)
+		return NULL;
+
+	return driver_name;
+}
+
+static void module_create_drivers_dir(struct module_kobject *mk)
+{
+	static DEFINE_MUTEX(drivers_dir_mutex);
+
+	mutex_lock(&drivers_dir_mutex);
+	if (mk && !mk->drivers_dir)
+		mk->drivers_dir = kobject_create_and_add("drivers", &mk->kobj);
+	mutex_unlock(&drivers_dir_mutex);
+}
+
+int module_add_driver(struct module *mod, const struct device_driver *drv)
+{
+	char *driver_name;
+	struct module_kobject *mk = NULL;
+	int ret;
+
+	if (!drv)
+		return 0;
+
+	if (mod)
+		mk = &mod->mkobj;
+	else if (drv->mod_name) {
+		/* Lookup or create built-in module entry in /sys/module */
+		mk = lookup_or_create_module_kobject(drv->mod_name);
+		if (mk) {
+			/* remember our module structure */
+			drv->p->mkobj = mk;
+			/* lookup_or_create_module_kobject took a reference */
+			kobject_put(&mk->kobj);
+		}
+	}
+
+	if (!mk)
+		return 0;
+
+	ret = sysfs_create_link(&drv->p->kobj, &mk->kobj, "module");
+	if (ret)
+		return ret;
+
+	driver_name = make_driver_name(drv);
+	if (!driver_name) {
+		ret = -ENOMEM;
+		goto out_remove_kobj;
+	}
+
+	module_create_drivers_dir(mk);
+	if (!mk->drivers_dir) {
+		ret = -EINVAL;
+		goto out_free_driver_name;
+	}
+
+	ret = sysfs_create_link(mk->drivers_dir, &drv->p->kobj, driver_name);
+	if (ret)
+		goto out_remove_drivers_dir;
+
+	kfree(driver_name);
+
+	return 0;
+
+out_remove_drivers_dir:
+	sysfs_remove_link(mk->drivers_dir, driver_name);
+
+out_free_driver_name:
+	kfree(driver_name);
+
+out_remove_kobj:
+	sysfs_remove_link(&drv->p->kobj, "module");
+	return ret;
+}
+
+void module_remove_driver(const struct device_driver *drv)
+{
+	struct module_kobject *mk = NULL;
+	char *driver_name;
+
+	if (!drv)
+		return;
+
+	sysfs_remove_link(&drv->p->kobj, "module");
+
+	if (drv->owner)
+		mk = &drv->owner->mkobj;
+	else if (drv->p->mkobj)
+		mk = drv->p->mkobj;
+	if (mk && mk->drivers_dir) {
+		driver_name = make_driver_name(drv);
+		if (driver_name) {
+			sysfs_remove_link(mk->drivers_dir, driver_name);
+			kfree(driver_name);
+		}
+	}
+}