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[103.168.172.201]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7e26996873esm111990585a.64.2025.07.13.22.37.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 13 Jul 2025 22:37:20 -0700 (PDT) Received: from phl-compute-04.internal (phl-compute-04.phl.internal [10.202.2.44]) by mailfauth.phl.internal (Postfix) with ESMTP id BEBCEF40066; Mon, 14 Jul 2025 01:37:19 -0400 (EDT) Received: from phl-mailfrontend-01 ([10.202.2.162]) by phl-compute-04.internal (MEProxy); Mon, 14 Jul 2025 01:37:19 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeeffedrtdefgdehuddufecutefuodetggdotefrod ftvfcurfhrohhfihhlvgemucfhrghsthforghilhdpuffrtefokffrpgfnqfghnecuuegr ihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjug hrpefhvfevufffkffojghfggfgsedtkeertdertddtnecuhfhrohhmpeeuohhquhhnucfh vghnghcuoegsohhquhhnrdhfvghnghesghhmrghilhdrtghomheqnecuggftrfgrthhtvg hrnhepgeeljeeitdehvdehgefgjeevfeejjeekgfevffeiueejhfeuiefggeeuheeggefg necuvehluhhsthgvrhfuihiivgepudenucfrrghrrghmpehmrghilhhfrhhomhepsghoqh hunhdomhgvshhmthhprghuthhhphgvrhhsohhnrghlihhthidqieelvdeghedtieegqddu jeejkeehheehvddqsghoqhhunhdrfhgvnhhgpeepghhmrghilhdrtghomhesfhhigihmvg drnhgrmhgvpdhnsggprhgtphhtthhopedvjedpmhhouggvpehsmhhtphhouhhtpdhrtghp thhtoheplhhinhhugidqkhgvrhhnvghlsehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtg hpthhtoheprhhushhtqdhfohhrqdhlihhnuhigsehvghgvrhdrkhgvrhhnvghlrdhorhhg pdhrtghpthhtoheplhhkmhhmsehlihhsthhsrdhlihhnuhigrdguvghvpdhrtghpthhtoh eplhhinhhugidqrghrtghhsehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtghpthhtohep ohhjvggurgeskhgvrhhnvghlrdhorhhgpdhrtghpthhtoheprghlvgigrdhgrgihnhhorh esghhmrghilhdrtghomhdprhgtphhtthhopegsohhquhhnrdhfvghnghesghhmrghilhdr tghomhdprhgtphhtthhopehgrghrhiesghgrrhihghhuohdrnhgvthdprhgtphhtthhope gsjhhorhhnfegpghhhsehprhhothhonhhmrghilhdrtghomh X-ME-Proxy: Feedback-ID: iad51458e:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Mon, 14 Jul 2025 01:37:17 -0400 (EDT) From: Boqun Feng To: linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, lkmm@lists.linux.dev, linux-arch@vger.kernel.org Cc: "Miguel Ojeda" , "Alex Gaynor" , "Boqun Feng" , "Gary Guo" , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= , "Benno Lossin" , "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 Subject: [PATCH v7 8/9] rust: sync: Add memory barriers Date: Sun, 13 Jul 2025 22:36:55 -0700 Message-Id: <20250714053656.66712-9-boqun.feng@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20250714053656.66712-1-boqun.feng@gmail.com> References: <20250714053656.66712-1-boqun.feng@gmail.com> Precedence: bulk X-Mailing-List: lkmm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Memory barriers are building blocks for concurrent code, hence provide a minimal set of them. The compiler barrier, barrier(), is implemented in inline asm instead of using core::sync::atomic::compiler_fence() because memory models are different: kernel's atomics are implemented in inline asm therefore the compiler barrier should be implemented in inline asm as well. Also it's currently only public to the kernel crate until there's a reasonable driver usage. Reviewed-by: Alice Ryhl Signed-off-by: Boqun Feng --- rust/helpers/barrier.c | 18 +++++++++++ rust/helpers/helpers.c | 1 + rust/kernel/sync.rs | 1 + rust/kernel/sync/barrier.rs | 61 +++++++++++++++++++++++++++++++++++++ 4 files changed, 81 insertions(+) create mode 100644 rust/helpers/barrier.c create mode 100644 rust/kernel/sync/barrier.rs diff --git a/rust/helpers/barrier.c b/rust/helpers/barrier.c new file mode 100644 index 000000000000..cdf28ce8e511 --- /dev/null +++ b/rust/helpers/barrier.c @@ -0,0 +1,18 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include + +void rust_helper_smp_mb(void) +{ + smp_mb(); +} + +void rust_helper_smp_wmb(void) +{ + smp_wmb(); +} + +void rust_helper_smp_rmb(void) +{ + smp_rmb(); +} diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c index 83e89f6a68fb..8ddfc8f84e87 100644 --- a/rust/helpers/helpers.c +++ b/rust/helpers/helpers.c @@ -9,6 +9,7 @@ #include "atomic.c" #include "auxiliary.c" +#include "barrier.c" #include "blk.c" #include "bug.c" #include "build_assert.c" diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs index b620027e0641..c7c0e552bafe 100644 --- a/rust/kernel/sync.rs +++ b/rust/kernel/sync.rs @@ -11,6 +11,7 @@ mod arc; pub mod atomic; +pub mod barrier; mod condvar; pub mod lock; mod locked_by; diff --git a/rust/kernel/sync/barrier.rs b/rust/kernel/sync/barrier.rs new file mode 100644 index 000000000000..8f2d435fcd94 --- /dev/null +++ b/rust/kernel/sync/barrier.rs @@ -0,0 +1,61 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Memory barriers. +//! +//! These primitives have the same semantics as their C counterparts: and the precise definitions +//! of semantics can be found at [`LKMM`]. +//! +//! [`LKMM`]: srctree/tools/memory-model/ + +/// A compiler barrier. +/// +/// A barrier that prevents compiler from reordering memory accesses across the barrier. +#[inline(always)] +pub(crate) fn barrier() { + // By default, Rust inline asms are treated as being able to access any memory or flags, hence + // it suffices as a compiler barrier. + // + // SAFETY: An empty asm block. + unsafe { core::arch::asm!("") }; +} + +/// A full memory barrier. +/// +/// A barrier that prevents compiler and CPU from reordering memory accesses across the barrier. +#[inline(always)] +pub fn smp_mb() { + if cfg!(CONFIG_SMP) { + // SAFETY: `smp_mb()` is safe to call. + unsafe { bindings::smp_mb() }; + } else { + barrier(); + } +} + +/// A write-write memory barrier. +/// +/// A barrier that prevents compiler and CPU from reordering memory write accesses across the +/// barrier. +#[inline(always)] +pub fn smp_wmb() { + if cfg!(CONFIG_SMP) { + // SAFETY: `smp_wmb()` is safe to call. + unsafe { bindings::smp_wmb() }; + } else { + barrier(); + } +} + +/// A read-read memory barrier. +/// +/// A barrier that prevents compiler and CPU from reordering memory read accesses across the +/// barrier. +#[inline(always)] +pub fn smp_rmb() { + if cfg!(CONFIG_SMP) { + // SAFETY: `smp_rmb()` is safe to call. + unsafe { bindings::smp_rmb() }; + } else { + barrier(); + } +} -- 2.39.5 (Apple Git-154)