linux-kernel - Re: [PATCH v5 4/5] rust: block: convert `block::mq` to use `Refcount`

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Message-ID: <aLZT9PQQyREAZuCm@tardis-2.local>
Date: Mon, 1 Sep 2025 19:18:28 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Benno Lossin <lossin@...nel.org>
Cc: Gary Guo <gary@...yguo.net>, Gary Guo <gary@...nel.org>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>, Will Deacon <will@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mark Rutland <mark.rutland@....com>,
	Tamir Duberstein <tamird@...il.com>,
	Francesco Zardi <frazar00@...il.com>,
	Antonio Hickey <contact@...oniohickey.com>,
	rust-for-linux@...r.kernel.org, David Gow <davidgow@...gle.com>,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/5] rust: block: convert `block::mq` to use `Refcount`

On Thu, Aug 28, 2025 at 09:18:40AM +0200, Benno Lossin wrote:
> On Wed Aug 27, 2025 at 9:51 PM CEST, Gary Guo wrote:
> > On Tue, 12 Aug 2025 10:17:44 +0200
> > "Benno Lossin" <lossin@...nel.org> wrote:
> >> On Thu Jul 24, 2025 at 1:32 AM CEST, Gary Guo wrote:
> >> > @@ -34,6 +36,18 @@ fn as_ptr(&self) -> *mut bindings::refcount_t {
> >> >          self.0.get()
> >> >      }
> >> >  
> >> > +    /// Get the underlying atomic counter that backs the refcount.
> >> > +    ///
> >> > +    /// NOTE: This will be changed to LKMM atomic in the future.  
> >> 
> >> Can we discourage using this function a bit more in the docs? At least
> >> point people to try other ways before reaching for this, since it allows
> >> overflowing & doesn't warn on saturate etc.
> >
> > Would this additional doc comment be good enough for you?
> >
> > /// NOTE: usage of this function is discouraged unless there is no way
> > /// to achieve the desired result using APIs in `refcount.h`. If an API
> > /// in `refcount.h` does not currently contain a binding, please
> > /// consider adding a binding for it instead.
> 
> I'd like to stress that the atomic doesn't have the same protections as
> the refcount type, how about:
> 
>     /// NOTE: usage of this function is discouraged as it can circumvent the protections offered by
>     /// `refcount.h`. If there is no way to achieve the result using APIs in `refcount.h`, then this
>     /// function can be used. Otherwise consider adding a binding for the required API.
> 

Looks good to me. I will apply this and some adjustment against my
atomic patchset, and queue this whole series for v6.18, thanks!

Regards,
Boqun

> ---
> Cheers,
> Benno