Re: [RFC PATCH v4 3/4] livepatch: Implement replace set for scoped atomic replace

On Wed, Aug 5, 2026 at 7:06 AM Song Liu <[email protected]> wrote:
>
> On Mon, Aug 3, 2026 at 11:50 PM Yafang Shao <[email protected]> wrote:
> [...]
> >  /*
> > - * Check that the new livepatch will not break the existing system states.
> > - * Cumulative patches must handle all already modified states.
> > - * Non-cumulative patches can touch already modified states.
> > + * Refuse loading a livepatch which would want to modify a
> > + * function which is already livepatched with the livepatch
> > + * with another "provides".
> >   */
>
> The comment above is not really accurate. This function doesn't
> really check "provides" or "obsoletes". Also, as long as the old
> patch's "provides" is in the new patches "obsoletes" or "provides",
> this replace is allowed (the comment doesn't mention "obsoletes". )

This is already handled by klp_patch_replaceable() in
klp_is_patch_compatible(). However, it would be clearer to move the
klp_patch_replaceable() check into klp_has_function_conflict() and
update the comments accordingly.

>
> > +static bool klp_has_function_conflict(struct klp_patch *patch,
> > +                                     struct klp_patch *old_patch)
> > +{
> > +       struct klp_object *obj, *old_obj;
> > +       struct klp_func *func;
> [...]
> >
> > +       # Always add provides ID to obsoletes (even if provides=0)
> > +       # This ensures the new patch replaces old patches with the same provides ID
>
> Do we really need th toolchain to enforce this? AFAICT, the kernel already
> guranteed "provides" means "obsoletes".

Dropping this enforcement simplifies the code logic. I will remove it
in the next version.

>
> Also, it will be great if we can add some basic tests for this. We are
> working on some new test framework for klp-build toolchain. But we
> don't have to wait for that. It is always good to add some tests for
> a major feature change.

Sure. I will add self tests in the next version.

-- 
Regards
Yafang