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linux-7.2.3/rust/kernel/sync/barrier.rs

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+// 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();
+    }
+}