[PATCH] rust: revocable: use LKMM atomics instead of Rust atomics

[Gary Guo]

From: Gary Guo <gary@xxxxxxxxxxx>

Kernel code should use LKMM atomics. The existing code is `AtomicBool` with
the need to use `xchg`, so convert it to `AtomicFlag`.

Signed-off-by: Gary Guo <gary@xxxxxxxxxxx>
---
 rust/kernel/revocable.rs | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/rust/kernel/revocable.rs b/rust/kernel/revocable.rs
index 2af212ea3b6d..4d177744520a 100644
--- a/rust/kernel/revocable.rs
+++ b/rust/kernel/revocable.rs
@@ -7,12 +7,22 @@
 
 use pin_init::Wrapper;
 
-use crate::{bindings, prelude::*, sync::rcu, types::Opaque};
+use crate::{
+    bindings,
+    prelude::*,
+    sync::{
+        atomic::{
+            AtomicFlag,
+            Relaxed, //
+        },
+        rcu, //
+    },
+    types::Opaque, //
+};
 use core::{
     marker::PhantomData,
     ops::Deref,
-    ptr::drop_in_place,
-    sync::atomic::{AtomicBool, Ordering},
+    ptr::drop_in_place, //
 };
 
 /// An object that can become inaccessible at runtime.
@@ -66,7 +76,7 @@
 /// ```
 #[pin_data(PinnedDrop)]
 pub struct Revocable<T> {
-    is_available: AtomicBool,
+    is_available: AtomicFlag,
     #[pin]
     data: Opaque<T>,
 }
@@ -85,7 +95,7 @@ impl<T> Revocable<T> {
     /// Creates a new revocable instance of the given data.
     pub fn new<E>(data: impl PinInit<T, E>) -> impl PinInit<Self, E> {
         try_pin_init!(Self {
-            is_available: AtomicBool::new(true),
+            is_available: AtomicFlag::new(true),
             data <- Opaque::pin_init(data),
         }? E)
     }
@@ -99,7 +109,7 @@ pub fn new<E>(data: impl PinInit<T, E>) -> impl PinInit<Self, E> {
     /// because another CPU may be waiting to complete the revocation of this object.
     pub fn try_access(&self) -> Option<RevocableGuard<'_, T>> {
         let guard = rcu::read_lock();
-        if self.is_available.load(Ordering::Relaxed) {
+        if self.is_available.load(Relaxed) {
             // Since `self.is_available` is true, data is initialised and has to remain valid
             // because the RCU read side lock prevents it from being dropped.
             Some(RevocableGuard::new(self.data.get(), guard))
@@ -117,7 +127,7 @@ pub fn try_access(&self) -> Option<RevocableGuard<'_, T>> {
     /// allowed to sleep because another CPU may be waiting to complete the revocation of this
     /// object.
     pub fn try_access_with_guard<'a>(&'a self, _guard: &'a rcu::Guard) -> Option<&'a T> {
-        if self.is_available.load(Ordering::Relaxed) {
+        if self.is_available.load(Relaxed) {
             // SAFETY: Since `self.is_available` is true, data is initialised and has to remain
             // valid because the RCU read side lock prevents it from being dropped.
             Some(unsafe { &*self.data.get() })
@@ -158,7 +168,7 @@ pub unsafe fn access(&self) -> &T {
     ///
     /// Callers must ensure that there are no more concurrent users of the revocable object.
     unsafe fn revoke_internal<const SYNC: bool>(&self) -> bool {
-        let revoke = self.is_available.swap(false, Ordering::Relaxed);
+        let revoke = self.is_available.xchg(false, Relaxed);
 
         if revoke {
             if SYNC {

base-commit: b8809969e1d7a591e0f49dd464a5d04b3cf02ab1
-- 
2.54.0