// 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(); } }