linux-kernel - Re: [PATCH 5/5] rust: sync: rcu: Add RCU protected pointer

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Message-ID: <aW2C-A5a7gfNENcb@tardis-2.local>
Date: Mon, 19 Jan 2026 09:03:52 +0800
From: Boqun Feng <boqun.feng@...il.com>
To: Dirk Behme <dirk.behme@...il.com>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
	rcu@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	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>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Josh Triplett <josh@...htriplett.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang@...ux.dev>,
	FUJITA Tomonori <fujita.tomonori@...il.com>
Subject: Re: [PATCH 5/5] rust: sync: rcu: Add RCU protected pointer

On Sun, Jan 18, 2026 at 09:28:35AM +0100, Dirk Behme wrote:
[...]
> > +    /// ```
> > +    pub fn dereference<'rcu>(&self, _rcu_guard: &'rcu Guard) -> Option<P::Borrowed<'rcu>> {
> > +        // Ordering: Address dependency pairs with the `store(Release)` in copy_update().
> > +        let ptr = self.as_atomic().load(Relaxed);
> > +
> > +        if !ptr.is_null() {
> > +            // SAFETY:
> 
> 
> Would it be an option to take an early return here and with this drop
> one indentation level of the larger `SAFETY` comment?
> 
> if ptr.is_null() {
>    return None;
> }
> 
> // SAFETY:
> ...
> Some(unsafe { P::borrow(ptr) })
> 
> Same for `Drop for Rcu<P>` below.
> 
> 

Make sense.

> > +            // - Since `ptr` is not null, so it has to be a return value of `P::into_foreign()`.
> > +            // - The returned `Borrowed<'rcu>` cannot outlive the RCU Guar, this guarantees the
> 
> Guar -> Guard
> 

Fixed! Thank you!

Regards,
Boqun