[PATCH] load_module: no BUG if module_subsys uninitialized

Invoking load_module() before param_sysfs_init() is called crashes in
mod_sysfs_setup(), since the kset in module_subsys is not initialized yet.

In my case, net-pf-1 is getting modprobed as a result of hotplug trying to
create a UNIX socket.  Calls to hotplug begin after the topology_init
initcall.

Another patch for the same symptom (module_subsys-initialize-earlier.patch)
moves param_sysfs_init() to the subsys initcalls, but this is still not
early enough in the boot process in some cases.  In particular,
topology_init() causes /sbin/hotplug to run, which requests net-pf-1 (the
UNIX socket protocol) which can be compiled as a module.  Moving
param_sysfs_init() to the postcore initcalls fixes this particular race,
but there might well be other cases where a usermodehelper causes a module
to load earlier still.

The patch makes load_module() return an error rather than crashing the
kernel if invoked before module_subsys is initialized.

Cc: Mark Huang <mlhuang@cs.princeton.edu>
Cc: Greg KH <greg@kroah.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/module.c

@@ -1054,6 +1054,12 @@ static int mod_sysfs_setup(struct module *mod,
 {
 	int err;
 
+	if (!module_subsys.kset.subsys) {
+		printk(KERN_ERR "%s: module_subsys not initialized\n",
+		       mod->name);
+		err = -EINVAL;
+		goto out;
+	}
 	memset(&mod->mkobj.kobj, 0, sizeof(mod->mkobj.kobj));
 	err = kobject_set_name(&mod->mkobj.kobj, "%s", mod->name);
 	if (err)