linux-kernel - Re: [PATCH 1/2] rust: sync: atomic: Remove bound `T: Sync` for `Atomci::from

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Message-Id: <DFTFW00MFONT.1WKK4LWVHUJL@garyguo.net>
Date: Tue, 20 Jan 2026 13:09:49 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "Boqun Feng" <boqun.feng@...il.com>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
 <kasan-dev@...glegroups.com>
Cc: "Will Deacon" <will@...nel.org>, "Peter Zijlstra"
 <peterz@...radead.org>, "Mark Rutland" <mark.rutland@....com>, "Gary Guo"
 <gary@...yguo.net>, "Miguel Ojeda" <ojeda@...nel.org>,
 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>, "Elle Rhumsaa" <elle@...thered-steel.dev>,
 "Paul E. McKenney" <paulmck@...nel.org>, "Marco Elver" <elver@...gle.com>,
 "FUJITA Tomonori" <fujita.tomonori@...il.com>
Subject: Re: [PATCH 1/2] rust: sync: atomic: Remove bound `T: Sync` for
 `Atomci::from_ptr()`

On Tue Jan 20, 2026 at 11:52 AM GMT, Boqun Feng wrote:
> Originally, `Atomic::from_ptr()` requires `T` being a `Sync` because I
> thought having the ability to do `from_ptr()` meant multiplle
> `&Atomic<T>`s shared by different threads, which was identical (or
> similar) to multiple `&T`s shared by different threads. Hence `T` was
> required to be `Sync`. However this is not true, since `&Atomic<T>` is
> not the same at `&T`. Moreover, having this bound makes `Atomic::<*mut
> T>::from_ptr()` impossible, which is definitely not intended. Therefore
> remove the `T: Sync` bound.
> 
> Fixes: 29c32c405e53 ("rust: sync: atomic: Add generic atomics")
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>

Title has "Atomci" instead of "Atomic"

Reviewed-by: Gary Guo <gary@...yguo.net>

> ---
>  rust/kernel/sync/atomic.rs | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)