Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx> --- rust/kernel/sync/atomic.rs | 23 +++++++++++++++++++++++ rust/kernel/sync/atomic/arch/arm64.rs | 20 ++++++++++++++++++++ rust/kernel/sync/atomic/arch/x86.rs | 5 +++++ 3 files changed, 48 insertions(+) diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index 280040705fb0..c3cae0d25e88 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -39,4 +39,27 @@ pub fn new(v: i32) -> Self { pub fn fetch_add_relaxed(&self, i: i32) -> i32 { arch::i32_fetch_add_relaxed(&self.0, i) } + + /// Subs `i` to the atomic variable with RELEASE ordering. + /// + /// Returns the old value before the sub. + /// + /// # Example + /// + /// ```rust + /// use kernel::sync::atomic::AtomicI32; + /// + /// let a = AtomicI32::new(1); + /// let b = a.fetch_sub_release(1); + /// let c = a.fetch_sub_release(2); + /// let d = a.fetch_sub_release(3); + /// let e = a.fetch_sub_release(core::i32::MIN); + /// + /// assert_eq!(b, 1); + /// assert_eq!(c, 0); + /// assert_eq!(d, -2); + /// ``` + pub fn fetch_sub_release(&self, i: i32) -> i32 { + arch::i32_fetch_sub_release(&self.0, i) + } } diff --git a/rust/kernel/sync/atomic/arch/arm64.rs b/rust/kernel/sync/atomic/arch/arm64.rs index 438f37cf7df6..beea77ecdb20 100644 --- a/rust/kernel/sync/atomic/arch/arm64.rs +++ b/rust/kernel/sync/atomic/arch/arm64.rs @@ -24,3 +24,23 @@ pub(crate) fn i32_fetch_add_relaxed(v: &UnsafeCell<i32>, i: i32) -> i32 { result } + +pub(crate) fn i32_fetch_sub_release(v: &UnsafeCell<i32>, i: i32) -> i32 { + let mut result; + unsafe { + asm!( + "prfm pstl1strm, [{v}]", + "1: ldxr {result:w}, [{v}]", + "sub {val:w}, {result:w}, {i:w}", + "stlxr {tmp:w}, {val:w}, [{v}]", + "cbnz {tmp:w}, 1b", + result = out(reg) result, + tmp = out(reg) _, + val = out(reg) _, + v = in(reg) v.get(), + i = in(reg) i, + ) + } + + result +} diff --git a/rust/kernel/sync/atomic/arch/x86.rs b/rust/kernel/sync/atomic/arch/x86.rs index 2d715f740b22..7f764cde4576 100644 --- a/rust/kernel/sync/atomic/arch/x86.rs +++ b/rust/kernel/sync/atomic/arch/x86.rs @@ -41,3 +41,8 @@ pub(crate) fn i32_fetch_add_relaxed(v: &UnsafeCell<i32>, i: i32) -> i32 { // SAFETY: `v.get()` points to a valid `i32`. unsafe { i32_xadd(v.get(), i) } } + +pub(crate) fn i32_fetch_sub_release(v: &UnsafeCell<i32>, i: i32) -> i32 { + // SAFETY: `v.get()` points to a valid `i32`. + unsafe { i32_xadd(v.get(), i.wrapping_neg()) } +} -- 2.44.0