Re: [PATCH V3] implement `ww_mutex` abstraction for the Rust tree

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Jun 19, 2025 at 04:44:01PM +0200, Alice Ryhl wrote:
> On Thu, Jun 19, 2025 at 4:33 PM Onur <work@onurozkan.dev> wrote:
> >
> > On Thu, 19 Jun 2025 16:14:01 +0200
> > Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > > On Thu, Jun 19, 2025 at 05:06:56PM +0300, Onur Özkan wrote:
> > > > +bool rust_helper_ww_mutex_is_locked(struct ww_mutex *lock)
> > > > +{
> > > > +   return ww_mutex_is_locked(lock);
> > > > +}
> > >
> > > Do we really need this? In general I dislike all the _is_locked()
> > > functions and would ideally like to remove them.
> > >
> > > Pretty much the only useful pattern for any of the _is_locked()
> > > functions is:
> > >
> > >   WARN_ON_ONCE(!foo_is_locked(&foo));
> > >
> > > Any other use is dodgy as heck.
> > >
> > >
> >
> > It's an abstraction of `ww_mutex_is_locked`. Since this is an
> > abstraction module, as long as `ww_mutex_is_locked` exists I think
> > we should keep it. FWIW it's also quite useful for tests.
> 
> We're not just adding copies of all of the C methods - instead we
> focus on the things we have a use-case for. If you're using them in
> tests, then that could make sense, but otherwise you shouldn't add
> them.

It might make sense to include the assert in the method. That is,
instead of providing .is_locked() that returns a boolean, have a void
method .assert_is_locked() that traps if not locked.