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 89BC8C2FF; Thu, 19 Feb 2026 12:20:21 +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=1771503621; cv=none; b=tmAEc6CBeFkAVKjMHvQ8lFpW84Dt592RQHwDsdMNncslCrtZbyg4PWxzaXsI0xfShs1t9WBTJ0nCw+F3e1J9khpQYvioE9rh0qSB4GWqkZer4plgxMHGV/shtbvQXwFLdR6NwQUPIDmXXJSGup3it7VenfBHN8C00vvxqopxywQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771503621; c=relaxed/simple; bh=XsWEzvzb57TvlQzTtZWNmidUcSKMJKtA/m2Kmmb0uhk=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=IDQ8ETmAkJ+xc1GfUi8RzM6efq5+gGBG+uof/OcR/VbC1Fff+xabtM8m9WLlvfUnuHzQJlN1G226y9ZfV/imWEN+M2bhdaoiAYY75RxzgWapaWJh5NuA2zB/DGc60tbg9wMQnBoI8A9lF6+ruJk0yFgl/LYwI9PA1VbDsFUZv+4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Zemx/y/n; 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="Zemx/y/n" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5C740C4CEF7; Thu, 19 Feb 2026 12:20:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771503621; bh=XsWEzvzb57TvlQzTtZWNmidUcSKMJKtA/m2Kmmb0uhk=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=Zemx/y/nW1fPpj4Yqn4moh/EW7jB/1Mi+04SU/hqyco/h3dmCtr3ZelgJ7Iuxq/5Q stHLmadwkNG0z4HefbvDLrTCCstLTjV4lRGvbrhvCTqsL7QcyEr+4emECoTHtI9390 hHp1z1vsEn5OENbwVa+PNtmU7p0aMmn2HiQMJJjRGKZd67Rbqz5azDmdJW2XOct9UX z3EwfgMuHFV57pHAKTqGS39RrIN1X+yqAgohHzxCFqX4HRuMQQ85sUnrjHW9hJtira 6qPFXt+H1CXt7gCjUuPyV9zhQTHIf0K885br1/NQRUH53e7oqRHs/j05f076TBU2mE B+4Ke4VP8gTew== From: Andreas Hindborg Date: Thu, 19 Feb 2026 13:20:09 +0100 Subject: [PATCH v2 1/2] rust: atomic: add fetch_sub Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260219-atomic-sub-v2-1-8bd99cadf26d@kernel.org> References: <20260219-atomic-sub-v2-0-8bd99cadf26d@kernel.org> In-Reply-To: <20260219-atomic-sub-v2-0-8bd99cadf26d@kernel.org> To: Will Deacon , Peter Zijlstra , Boqun Feng , Mark Rutland , Gary Guo , Miguel Ojeda , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Alice Ryhl , Trevor Gross , Danilo Krummrich Cc: linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, Andreas Hindborg X-Mailer: b4 0.15-dev X-Developer-Signature: v=1; a=openpgp-sha256; l=3236; i=a.hindborg@kernel.org; h=from:subject:message-id; bh=XsWEzvzb57TvlQzTtZWNmidUcSKMJKtA/m2Kmmb0uhk=; b=owEBbQKS/ZANAwAKAeG4Gj55KGN3AcsmYgBplv/61sNywcGwm8GZSlnDcvdg1gaiuZQQyytnA SLWKdfNmnKJAjMEAAEKAB0WIQQSwflHVr98KhXWwBLhuBo+eShjdwUCaZb/+gAKCRDhuBo+eShj dyqOEACj7QH+77pj4RA7Nky+7A+hK0wUH4Ci/wfrs7vJnR/0R/d8QcKICVRDc8qKURTZUWJY05C A7zsBzwGJwbQtQT90oh1Eo13Ppve9sIo2Fk7HtKIkLtNtEKhOC7VfzKZJ2h9SG1OV8gBDEFIf34 5yU+etWVeucoaDm2IEidQ6e05HjnibK+Mjk5plwg4CdM5XM2RhMV5DW7jhwZJPDVRLSH1awVDXc /izswEvVPrBdvfEhhSY4M+pSfRbFdye1QN6kEqcSYO45Nr8W4Bk7b4pZGxlvbA9UYz9NC7uz+vx IWFPEYljnzWyx57eflpw5NRzleyx6gKY62SFfO8f6VuqkQ+SvZKGrM5PcMIXBy76d8KNrajB7if IWYWKO6BaD5mfOmajT75iGp9ckJ40Nf1Svw08qra0cwBJLyd1iZMuk8AoxgECouNXToIQaNj4PU 8xuDyqG3ZmP6zpi3fOjLiO1Ece4E93SXPbu64WkU0uzIn4UNh9W3XOQ3RLAmMIy9wksJY7AdBYd Ybt44c0yiTjGuSa0Gu3E/Tp/0G22+02Htu/fDM136NOVO/2RCvVdW7aH+qCds5NbPqDmcxUfcRn xIZMDWDaEzvtfWempObGWJTwAbK2HLlML9DUiw57iJN5RkOkFSr3qM85Yo6bZtbXyGEWN/ossA5 IKaGZsHEJaoAAlw== X-Developer-Key: i=a.hindborg@kernel.org; a=openpgp; fpr=3108C10F46872E248D1FB221376EB100563EF7A7 Add `Atomic::fetch_sub` with implementation and documentation in line with existing `Atomic::fetch_add` implementation. Reviewed-by: Alice Ryhl Signed-off-by: Andreas Hindborg --- rust/kernel/sync/atomic.rs | 43 +++++++++++++++++++++++++++++++++++++ rust/kernel/sync/atomic/internal.rs | 5 +++++ 2 files changed, 48 insertions(+) diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index 4aebeacb961a2..83e03bb7ecd24 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -559,4 +559,47 @@ pub fn fetch_add(&self, v: Rhs, _: Ordering) // SAFETY: `ret` comes from reading `self.0`, which is a valid `T` per type invariants. unsafe { from_repr(ret) } } + + /// Atomic fetch and subtract. + /// + /// Atomically updates `*self` to `(*self).wrapping_sub(v)`, and returns the value of `*self` + /// before the update. + /// + /// # Examples + /// + /// ``` + /// use kernel::sync::atomic::{Atomic, Acquire, Full, Relaxed}; + /// + /// let x = Atomic::new(42); + /// assert_eq!(42, x.load(Relaxed)); + /// assert_eq!(42, x.fetch_sub(12, Acquire)); + /// assert_eq!(30, x.load(Relaxed)); + /// + /// let x = Atomic::new(42); + /// assert_eq!(42, x.load(Relaxed)); + /// assert_eq!(42, x.fetch_sub(12, Full)); + /// assert_eq!(30, x.load(Relaxed)); + /// ``` + #[inline(always)] + pub fn fetch_sub(&self, v: Rhs, _: Ordering) -> T + where + // Types that support addition also support subtraction. + T: AtomicAdd, + { + let v = T::rhs_into_delta(v); + + // INVARIANT: `self.0` is a valid `T` after `atomic_fetch_sub*()` due to safety requirement + // of `AtomicAdd`. + let ret = { + match Ordering::TYPE { + OrderingType::Full => T::Repr::atomic_fetch_sub(&self.0, v), + OrderingType::Acquire => T::Repr::atomic_fetch_sub_acquire(&self.0, v), + OrderingType::Release => T::Repr::atomic_fetch_sub_release(&self.0, v), + OrderingType::Relaxed => T::Repr::atomic_fetch_sub_relaxed(&self.0, v), + } + }; + + // SAFETY: `ret` comes from reading `self.0`, which is a valid `T` per type invariants. + unsafe { from_repr(ret) } + } } diff --git a/rust/kernel/sync/atomic/internal.rs b/rust/kernel/sync/atomic/internal.rs index 6fdd8e59f45be..7eed8c66efff8 100644 --- a/rust/kernel/sync/atomic/internal.rs +++ b/rust/kernel/sync/atomic/internal.rs @@ -261,5 +261,10 @@ fn fetch_add[acquire, release, relaxed](a: &AtomicRepr, v: Self::Delta) -> // SAFETY: `a.as_ptr()` is valid and properly aligned. unsafe { bindings::#call(v, a.as_ptr().cast()) } } + + fn fetch_sub[acquire, release, relaxed](a: &AtomicRepr, v: Self::Delta) -> Self { + // SAFETY: `a.as_ptr()` is valid and properly aligned. + unsafe { bindings::#call(v, a.as_ptr().cast()) } + } } ); -- 2.51.2