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

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Message-ID: <aW93VwfgkHpJfjVs@google.com>
Date: Tue, 20 Jan 2026 12:38:47 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, kasan-dev@...glegroups.com, 
	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>, 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 07:52:06PM +0800, 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>

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>