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 9313A21C173; Tue, 6 Jan 2026 12:29:44 +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=1767702584; cv=none; b=c3YXzGGO5mc1U1wtyVYzLfDYMb958JlikotHsbMRNB2/28J0ojaGoTFICteOmQRZWAjU7JiZ3uFLn2nqyKGwE17lwDZp+lc4b5bpnZO0Cifa2UHMpDcCQeoaRB7ZLrVsghXV98aZkwCnt66J4xGVJwXmLH4czJlH61Ot657TjZE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767702584; c=relaxed/simple; bh=KdLZFYMo7D4KPX3nlmpFQNO3qXfuSWZLiNfCSlwfPFs=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=hTzhsEQSCWZxva7wIUbpbf5+v1voUuk9KNYIMgBhk+vJlY5rEJsEtwhgvfT7nhxQo3lnYQ7k0NwlQCeKVQcyr34HiMrl/YrTSHpvZob00i1w+KpWz5Gb9dz+bHsIdTkwSf9z/C/fQGy1o0Pv3y35OF3GnVqpixWZy1V0Bkl36VI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pfmeexpe; 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="pfmeexpe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3AB00C116C6; Tue, 6 Jan 2026 12:29:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767702584; bh=KdLZFYMo7D4KPX3nlmpFQNO3qXfuSWZLiNfCSlwfPFs=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=pfmeexpeommc0Z48KlHkDG+vbHD/HruwhVAn3NqZGVnyBH0q8cTWnjEnC6jLAKhEP jvGy9/jGZZvzp+gux1eyb+yT1Y21KLh7LvupU4FVf0sRD9EggxFzdKaGFnIf3F4DIc MJgNmmmp7bsFzYdFKH5FsK6NX992jTJ+2IRNWDpjW8CPhuJuSVm3joTb8p0Vf2tHgt JKfh3EnCbayBEGjSHwsu4TtWtzQ0weOduCoWft58+nVg5hzboV+vNbEwbdCuIXLXnt 0iAL5MF2RD8kWQ1IsoKAnbedMhBjuvsICZo/iLuYgmbZEFF+vWYyqInnffH1UPAyH/ CO2a7CY28Nd+Q== From: Andreas Hindborg To: Alice Ryhl , Boqun Feng , Will Deacon , Peter Zijlstra Cc: Richard Henderson , Matt Turner , Magnus Lindholm , Catalin Marinas , Miguel Ojeda , Gary Guo , =?utf-8?Q?Bj=C3=B6rn?= Roy Baron , Benno Lossin , Trevor Gross , Danilo Krummrich , Mark Rutland , FUJITA Tomonori , Frederic Weisbecker , Lyude Paul , Thomas Gleixner , Anna-Maria Behnsen , John Stultz , Stephen Boyd , Alexander Viro , Christian Brauner , Jan Kara , linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org, Alice Ryhl Subject: Re: [PATCH 2/5] rust: sync: add READ_ONCE and WRITE_ONCE In-Reply-To: <20251231-rwonce-v1-2-702a10b85278@google.com> References: <20251231-rwonce-v1-0-702a10b85278@google.com> <20251231-rwonce-v1-2-702a10b85278@google.com> Date: Tue, 06 Jan 2026 13:29:11 +0100 Message-ID: <87ldiaj560.fsf@t14s.mail-host-address-is-not-set> Precedence: bulk X-Mailing-List: linux-alpha@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain "Alice Ryhl" writes: > There are currently a few places in the kernel where we use volatile > reads when we really should be using `READ_ONCE`. To make it possible to > replace these with proper `READ_ONCE` calls, introduce a Rust version of > `READ_ONCE`. > > I've written the code to use Rust's volatile ops directly when possible. > This results in a small amount of code duplication, but I think it makes > sense for READ_ONCE and WRITE_ONCE to be implemented in pure Rust when > possible. Otherwise they would unconditionally be a function call unless > you have a system where you can perform cross-language inlining. > > I considered these functions in the bindings crate instead of kernel > crate. I actually think it would make a lot of sense. But it implies > some annoying complications on old compilers since the #![feature()] > invocations in kernel/lib.rs do not apply in the bindings crate. > > For now, we do not support using READ_ONCE on compound types even if > they have the right size. This can be added later. > > This fails checkpatch due to a misordered MAINTAINERS entry, but this is > a pre-existing problem. > > Signed-off-by: Alice Ryhl > --- > MAINTAINERS | 2 + > rust/helpers/helpers.c | 1 + > rust/helpers/rwonce.c | 34 ++++++++ > rust/kernel/sync.rs | 2 + > rust/kernel/sync/rwonce.rs | 188 +++++++++++++++++++++++++++++++++++++++++++++ > 5 files changed, 227 insertions(+) > > diff --git a/MAINTAINERS b/MAINTAINERS > index 12f49de7fe036c2439c00f9f4c67b2219d72a4c3..1d0cae158fe2cc7d99b6a64c11176b635e2d14e4 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -4117,9 +4117,11 @@ F: arch/*/include/asm/atomic*.h > F: include/*/atomic*.h > F: include/linux/refcount.h > F: scripts/atomic/ > +F: rust/helpers/rwonce.c > F: rust/kernel/sync/atomic.rs > F: rust/kernel/sync/atomic/ > F: rust/kernel/sync/refcount.rs > +F: rust/kernel/sync/rwonce.rs > > ATTO EXPRESSSAS SAS/SATA RAID SCSI DRIVER > M: Bradley Grove > diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c > index 79c72762ad9c4b473971e6210c9577860d2e2b08..28b79ca7844fb744e5ad128238824921c055ec82 100644 > --- a/rust/helpers/helpers.c > +++ b/rust/helpers/helpers.c > @@ -48,6 +48,7 @@ > #include "rcu.c" > #include "refcount.c" > #include "regulator.c" > +#include "rwonce.c" > #include "scatterlist.c" > #include "security.c" > #include "signal.c" > diff --git a/rust/helpers/rwonce.c b/rust/helpers/rwonce.c > new file mode 100644 > index 0000000000000000000000000000000000000000..55c621678cd632e728cb925b6a4a2e34e2fc4884 > --- /dev/null > +++ b/rust/helpers/rwonce.c > @@ -0,0 +1,34 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +/* > + * Copyright (C) 2025 Google LLC. > + */ > + > +#ifdef CONFIG_ARCH_USE_CUSTOM_READ_ONCE > + > +__rust_helper u8 rust_helper_read_once_1(const u8 *ptr) > +{ > + return READ_ONCE(*ptr); > +} > + > +__rust_helper u16 rust_helper_read_once_2(const u16 *ptr) > +{ > + return READ_ONCE(*ptr); > +} > + > +__rust_helper u32 rust_helper_read_once_4(const u32 *ptr) > +{ > + return READ_ONCE(*ptr); > +} > + > +__rust_helper u64 rust_helper_read_once_8(const u64 *ptr) > +{ > + return READ_ONCE(*ptr); > +} > + > +__rust_helper void *rust_helper_read_once_ptr(void * const *ptr) > +{ > + return READ_ONCE(*ptr); > +} > + > +#endif > diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs > index 5df87e2bd212e192b8a67644bd99f05b9d4afd75..a5bf7bdc3fa8a044786eafae39fe8844aeeef057 100644 > --- a/rust/kernel/sync.rs > +++ b/rust/kernel/sync.rs > @@ -20,6 +20,7 @@ > pub mod poll; > pub mod rcu; > mod refcount; > +pub mod rwonce; > mod set_once; > > pub use arc::{Arc, ArcBorrow, UniqueArc}; > @@ -30,6 +31,7 @@ > pub use lock::spinlock::{new_spinlock, SpinLock, SpinLockGuard}; > pub use locked_by::LockedBy; > pub use refcount::Refcount; > +pub use rwonce::{READ_ONCE, WRITE_ONCE}; > pub use set_once::SetOnce; > > /// Represents a lockdep class. It's a wrapper around C's `lock_class_key`. > diff --git a/rust/kernel/sync/rwonce.rs b/rust/kernel/sync/rwonce.rs > new file mode 100644 > index 0000000000000000000000000000000000000000..a1660e43c9ef94011812d1816713cf031a73de1d > --- /dev/null > +++ b/rust/kernel/sync/rwonce.rs > @@ -0,0 +1,188 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +// Copyright (C) 2025 Google LLC. > + > +//! Rust version of the raw `READ_ONCE`/`WRITE_ONCE` functions. > +//! > +//! C header: [`include/asm-generic/rwonce.h`](srctree/include/asm-generic/rwonce.h) > + > +/// Read the pointer once. > +/// > +/// # Safety > +/// > +/// It must be safe to `READ_ONCE` the `ptr` with this type. > +#[inline(always)] > +#[must_use] > +#[track_caller] > +#[expect(non_snake_case)] I really do not think we need to have screaming snake case here. I understand that this is what the macro looks like in C code, but we do not need to carry that over. Best regards, Andreas Hindborg