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

From: Gary Guo
Date: Fri Oct 04 2024 - 15:53:35 EST


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

> Hi Gary,
>
> "Gary Guo" <gary@xxxxxxxxxxx> 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