From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B2EF32594B4; Mon, 14 Jul 2025 15:05:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752505547; cv=none; b=ZwtG4nmYUChg3Y4oYjCjckPLmVCLCd+uxBF9fJDTq0IUgL+kdoFzBPZ5kfjCT9eyvb4PtysDbYo0KiTUxoYOyFUGRqOIUUsujiyOQ9qhzKQKt2GQsRWRs2KSSyF/SemSDPT+WnW3hgivTsVnPRxkfFsPf2U3lYYEBizOGj3MjPw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752505547; c=relaxed/simple; bh=8JHF2oaX32pB33OO8iIS6R4334am5Qgv2ejcIuPp9o0=; h=Mime-Version:Content-Type:Date:Message-Id:Subject:From:To:Cc: References:In-Reply-To; b=NrAvd5SjniD3fe0b6WuLLJMMrtRxTv3chWJnRULgt9CHwuwaueaGpVkZQYhWIJ2nvINFY1NyhPNTLGupbYt6phUbK1nlNjhWWUiDNAcas4lUsfhSJcFF8VgKXyMDy+KzzI53V5kQfoMRp0drap7rYxpuHHCp9g41R5gPhhGO4OI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=J/HjJTwg; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="J/HjJTwg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4A804C4CEF6; Mon, 14 Jul 2025 15:05:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1752505547; bh=8JHF2oaX32pB33OO8iIS6R4334am5Qgv2ejcIuPp9o0=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=J/HjJTwg/JgRiWr8w9WBD8IyNRroWC6BjFDwFoNFoBLaIRBmMtiZWsd8+ayvrRXQA RSYcfZ3dK4UbbyDormP5SPFa1+OC1QNV6/paCERfTD/onVtxorxcS9spSTEU2pWdsH GccNObc6Xrm6CwEu4+1ruB1dV8UxQ8t6yWi5Rp8xSJpEUuosOf95Kw3Js4PZHZkkSO qc5OSt4oGhpskf1Re83u3YwTOzqx56SBDvwVxsnPkO2a7xJPWMERw63/wSyOjWaY6p +fhr8XnC7CnM+LTTXDhH4HfcjseChxnv7FGFEKYX8rW9TAnsK0DNB3+7eh/+GjIOA3 WE6nOi4iwt6ng== Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 14 Jul 2025 17:05:40 +0200 Message-Id: Subject: Re: [PATCH v7 4/9] rust: sync: atomic: Add generic atomics From: "Benno Lossin" To: "Boqun Feng" Cc: , , , , "Miguel Ojeda" , "Alex Gaynor" , "Gary Guo" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Andreas Hindborg" , "Alice Ryhl" , "Trevor Gross" , "Danilo Krummrich" , "Will Deacon" , "Peter Zijlstra" , "Mark Rutland" , "Wedson Almeida Filho" , "Viresh Kumar" , "Lyude Paul" , "Ingo Molnar" , "Mitchell Levy" , "Paul E. McKenney" , "Greg Kroah-Hartman" , "Linus Torvalds" , "Thomas Gleixner" , "Alan Stern" X-Mailer: aerc 0.20.1 References: <20250714053656.66712-1-boqun.feng@gmail.com> <20250714053656.66712-5-boqun.feng@gmail.com> In-Reply-To: On Mon Jul 14, 2025 at 4:21 PM CEST, Boqun Feng wrote: > On Mon, Jul 14, 2025 at 12:30:12PM +0200, Benno Lossin wrote: >> On Mon Jul 14, 2025 at 7:36 AM CEST, Boqun Feng wrote: >> > To provide using LKMM atomics for Rust code, a generic `Atomic` is >> > added, currently `T` needs to be Send + Copy because these are the >> > straightforward usages and all basic types support this. >> > >> > Implement `AllowAtomic` for `i32` and `i64`, and so far only basic >> > operations load() and store() are introduced. >> > >> > Reviewed-by: Alice Ryhl >> > Signed-off-by: Boqun Feng >> > --- >> > rust/kernel/sync/atomic.rs | 14 ++ >> > rust/kernel/sync/atomic/generic.rs | 285 ++++++++++++++++++++++++++++= + >> > 2 files changed, 299 insertions(+) >> > create mode 100644 rust/kernel/sync/atomic/generic.rs >> > >> > diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs >> > index e80ac049f36b..c5193c1c90fe 100644 >> > --- a/rust/kernel/sync/atomic.rs >> > +++ b/rust/kernel/sync/atomic.rs >> > @@ -16,7 +16,21 @@ >> > //! >> > //! [`LKMM`]: srctree/tools/memory-model/ >> > =20 >> > +pub mod generic; >>=20 >> Hmm, maybe just re-export the stuff? I don't think there's an advantage >> to having the generic module be public. >>=20 > > If `generic` is not public, then in the kernel::sync::atomic page, it > won't should up, and there is no mentioning of struct `Atomic` either. > > If I made it public and also re-export the `Atomic`, there would be a > "Re-export" section mentioning all the re-exports, so I will keep > `generic` unless you have some tricks that I don't know. Just use `#[doc(inline)]` :) https://doc.rust-lang.org/rustdoc/write-documentation/the-doc-attribute= .html#inline-and-no_inline > Also I feel it's a bit naturally that `AllowAtomic` and `AllowAtomicAdd` > stay under `generic` (instead of re-export them at `atomic` mod level) > because they are about the generic part of `Atomic`, right? Why is that more natural? It only adds an extra path layer in any import for atomics. Unless you at some point want to add `concrete::Atomic` etc, I would just re-export them. >> > +/// The atomic operations are implemented in a way that is fully comp= atible with the [Linux Kernel >> > +/// Memory (Consistency) Model][LKMM], hence they should be modeled a= s the corresponding >> > +/// [`LKMM`][LKMM] atomic primitives. With the help of [`Atomic::from= _ptr()`] and >> > +/// [`Atomic::as_ptr()`], this provides a way to interact with [C-sid= e atomic operations] >> > +/// (including those without the `atomic` prefix, e.g. `READ_ONCE()`,= `WRITE_ONCE()`, >> > +/// `smp_load_acquire()` and `smp_store_release()`). >> > +/// >> > +/// [LKMM]: srctree/tools/memory-model/ >> > +/// [C-side atomic operations]: srctree/Documentation/atomic_t.txt >>=20 >> Did you check that these links looks good in rustdoc? >>=20 > > Yep. Nice :) >> > +/// over unit-only enums, see [Examples]. >> > +/// >> > +/// # Limitations >> > +/// >> > +/// Because C primitives are used to implement the atomic operations,= and a C function requires a >> > +/// valid object of a type to operate on (i.e. no `MaybeUninit<_>`), = hence at the Rust <-> C >> > +/// surface, only types with no uninitialized bits can be passed. As = a result, types like `(u8, >>=20 >> s/no uninitialized/initialized/ >>=20 > > hmm.. "with initialized bits" seems to me saying "it's OK as long as > some bits are initialized", how about "with all the bits initialized"? Sounds good. The double negation sounded a bit weird to me. >> > + /// However, this should be only used when communicating with C s= ide or manipulating a C >> > + /// struct. >>=20 >> This sentence should be above the `Safety` section. >>=20 > > Hmm.. why? This is the further information about what the above > "Examples" section just mentioned? I thought "this" is referring to "this function", if not then please be more concrete :) --- Cheers, Benno