rust: revocable: use LKMM atomics instead of Rust atomics

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

Posted by Gary Guo 1 week, 2 days ago

From: Gary Guo <gary@garyguo.net>

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@garyguo.net>
---
 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

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

Posted by Boqun Feng an hour ago

On Thu, Jul 16, 2026 at 03:55:35PM +0100, Gary Guo wrote:
> From: Gary Guo <gary@garyguo.net>
> 
> 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@garyguo.net>

Queued it in rust-sync, thank you all!

Regards,
Boqun

> ---
>  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
>

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

Posted by Alice Ryhl 2 days, 21 hours ago

On Thu, Jul 16, 2026 at 4:56 PM Gary Guo <gary@kernel.org> wrote:
>
> From: Gary Guo <gary@garyguo.net>
>
> 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@garyguo.net>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

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

Posted by FUJITA Tomonori 1 week, 1 day ago

On Thu, 16 Jul 2026 15:55:35 +0100
Gary Guo <gary@kernel.org> wrote:

> From: Gary Guo <gary@garyguo.net>
> 
> 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@garyguo.net>
> ---
>  rust/kernel/revocable.rs | 26 ++++++++++++++++++--------
>  1 file changed, 18 insertions(+), 8 deletions(-)

Reviewed-by: FUJITA Tomonori <fujita.tomonori@gmail.com>