Re: [PATCH 3/3] rust: block: convert `block::mq` to use `Refcount`

[Gary Guo <gary@garyguo.net>]

On Fri, 04 Oct 2024 20:34:01 +0200
Andreas Hindborg <a.hindborg@kernel.org> wrote:

> Hi Gary,
> 
> "Gary Guo" <gary@garyguo.net> writes:
> 
> [...]
> 
> >  // SAFETY: All instances of `Request<T>` are reference counted. This
> >  // implementation of `AlwaysRefCounted` ensure that increments to the ref count
> >  // keeps the object alive in memory at least until a matching reference count
> >  // decrement is executed.
> >  unsafe impl<T: Operations> AlwaysRefCounted for Request<T> {
> >      fn inc_ref(&self) {
> > -        let refcount = &self.wrapper_ref().refcount();
> > -
> > -        #[cfg_attr(not(CONFIG_DEBUG_MISC), allow(unused_variables))]
> > -        let updated = atomic_relaxed_op_unless(refcount, |x| x + 1, 0);
> > -
> > -        #[cfg(CONFIG_DEBUG_MISC)]
> > -        if !updated {
> > -            panic!("Request refcount zero on clone")
> > -        }
> > +        self.wrapper_ref().refcount().inc();  
> 
> What happened to the debug code?
> 
> 
> BR Andreas
> 

`refcount_inc` will WARN and saturate the refcount when trying to
increment from zero. This is true regardless of config.

I've already captured this in `Refcount::inc` documentation.

Best,
Gary