Re: [PATCH 3/3] rv/reactors: add KUnit tests for reactor_panic

[Gabriele Monaco <gmonaco@redhat.com>]

On Fri, 2026-07-10 at 00:46 +0800, Wen Yang wrote:
> Since rv_panic_reaction calls vpanic() which is __noreturn, direct 
> testing is not feasible in KUnit.
> 
> A preparatory v2 drops reactor_printk_kunit.c and reactor_panic_kunit.c
> entirely, replacing them with a single rv_reactors_kunit.c containing
> two suites:
> 
>    rv_reactor_registration: register/unregister lifecycle, duplicate
>      rejection (-EINVAL), name-too-long rejection, and safe unregister
>      of a never-registered reactor.
> 
>    rv_react_dispatch: null-callback guard, callback invocation check,
>      and the mdelay lockdep stress test.
> 
> 
> v2 also adds EXPORT_SYMBOL_GPL for rv_react(), rv_register_reactor(), 
> and rv_unregister_reactor(), and the Kconfig entry is tristate.

Alright, sounds good.

> Additional fix: rv_unregister_reactor()
> 
> Testing exposed a real bug: rv_unregister_reactor() called list_del()
> unconditionally.  On a never-registered reactor the list_head is
> zero-initialised, so list_del() dereferences NULL->prev and crashes.
> v2 adds a patch that iterates rv_reactors_list first and only calls
> list_del() when the reactor is found.  test_unregister_nonexistent
> documents and guards this behaviour.

Mmh, besides unit testing, when can we even see a reactor unregistration before
it's ever registered? Do we really need to actively guard against this?

What is probably an issue is to call unregistration also if registration failed
in reactors (which would cause the /bug/ you see, but shouldn't happen on
current reactors anyway), we can fix that.

I wouldn't guard against an issue that can only be triggered by broken code.
What am I missing?

Thanks,
Gabriele