module: don't ignore sysfs_create_link() failures

The sysfs_create_link() return code is marked as __must_check, but the
module_add_driver() function tries hard to not care, by assigning the
return code to a variable. When building with 'make W=1', gcc still
warns because this variable is only assigned but not used:

drivers/base/module.c: In function 'module_add_driver':
drivers/base/module.c:36:6: warning: variable 'no_warn' set but not used [-Wunused-but-set-variable]

Rework the code to properly unwind and return the error code to the
caller. My reading of the original code was that it tries to
not fail when the links already exist, so keep ignoring -EEXIST
errors.

Fixes: e17e0f51aeea ("Driver core: show drivers in /sys/module/")
See-also: 4a7fb6363f2d ("add __must_check to device management code")
Signed-off-by: Arnd Bergmann <[e-mail]>
Reviewed-by: Luis Chamberlain <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/base.h

···
 void devices_kset_move_last(struct device *dev);
 
 #if defined(CONFIG_MODULES) && defined(CONFIG_SYSFS)
-void module_add_driver(struct module *mod, struct device_driver *drv);
+int module_add_driver(struct module *mod, struct device_driver *drv);
 void module_remove_driver(struct device_driver *drv);
 #else
-static inline void module_add_driver(struct module *mod,
-				     struct device_driver *drv) { }
+static inline int module_add_driver(struct module *mod,
+				    struct device_driver *drv)
+{
+	return 0;
+}
 static inline void module_remove_driver(struct device_driver *drv) { }
 #endif
 

drivers/base/bus.c

···
 		if (error)
 			goto out_del_list;
 	}
-	module_add_driver(drv->owner, drv);
+	error = module_add_driver(drv->owner, drv);
+	if (error) {
+		printk(KERN_ERR "%s: failed to create module links for %s\n",
+			__func__, drv->name);
+		goto out_detach;
+	}
 
 	error = driver_create_file(drv, &driver_attr_uevent);
 	if (error) {
···
 
 	return 0;
 
+out_detach:
+	driver_detach(drv);
 out_del_list:
 	klist_del(&priv->knode_bus);
 out_unregister:

drivers/base/module.c

···
 	mutex_unlock(&drivers_dir_mutex);
 }
 
-void module_add_driver(struct module *mod, struct device_driver *drv)
+int module_add_driver(struct module *mod, struct device_driver *drv)
 {
 	char *driver_name;
-	int no_warn;
 	struct module_kobject *mk = NULL;
+	int ret;
 
 	if (!drv)
-		return;
+		return 0;
 
 	if (mod)
 		mk = &mod->mkobj;
···
 	}
 
 	if (!mk)
-		return;
+		return 0;
 
-	/* Don't check return codes; these calls are idempotent */
-	no_warn = sysfs_create_link(&drv->p->kobj, &mk->kobj, "module");
+	ret = sysfs_create_link(&drv->p->kobj, &mk->kobj, "module");
+	if (ret)
+		return ret;
+
 	driver_name = make_driver_name(drv);
-	if (driver_name) {
-		module_create_drivers_dir(mk);
-		no_warn = sysfs_create_link(mk->drivers_dir, &drv->p->kobj,
-					    driver_name);
-		kfree(driver_name);
+	if (!driver_name) {
+		ret = -ENOMEM;
+		goto out;
 	}
+
+	module_create_drivers_dir(mk);
+	if (!mk->drivers_dir) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	ret = sysfs_create_link(mk->drivers_dir, &drv->p->kobj, driver_name);
+	if (ret)
+		goto out;
+
+	kfree(driver_name);
+
+	return 0;
+out:
+	sysfs_remove_link(&drv->p->kobj, "module");
+	sysfs_remove_link(mk->drivers_dir, driver_name);
+	kfree(driver_name);
+
+	return ret;
 }
 
 void module_remove_driver(struct device_driver *drv)