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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();
}
}
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