Re: [PATCH v13 04/12] livepatch: Consolidate klp_free functions

Miroslav Benes
2018-11-21T13:59:33Z

> -/*
> - * Free all functions' kobjects in the array up to some limit. When limit is
> - * NULL, all kobjects are freed.
> - */
> -static void klp_free_funcs_limited(struct klp_object *obj,
> - struct klp_func *limit)
> +static void klp_free_funcs(struct klp_object *obj)
> {
> struct klp_func *func;
>
> - for (func = obj->funcs; func->old_name && func != limit; func++)
> - kobject_put(&func->kobj);
> + klp_for_each_func(obj, func) {
> + /* Might be called from klp_init_patch() error path. */
> + if (func->kobj.state_initialized)
> + kobject_put(&func->kobj);
> + }
> }

I have not noticed till today, but state_initialized is probably not the
best idea. kobject_init_and_add() sets it to 1 in kobject_init() part but
then _add() is called which could result in error. So we would end up with
state_initialized equal to 1 and kobject reference equal to 0. Later call
to kobject_put() in klp_free_funcs() (or elsewhere) would not call
->release method, because refcount would be 0 by then.

I think that all would end up well, but that does not mean we should not
fix it.

We could use state_in_sysfs, but I do not think it guarantees anything.
Both are internal states and maybe we should not rely on them.

So kref_read() and check the reference?

Miroslav