[PATCH v3 0/3] Add and use abstraction for synchronize_rcu()

[PATCH v3 0/3] Add and use abstraction for synchronize_rcu()

[Philipp Stanner]

Changes since v2:
  - Compromise docu for "RCU versus atomic context" a bit better
  - Add respective R-b's

Changes since v1:
  - Vertically format imports. (Onur)
  - Make the new function #[inline]. (Alice)
  - Add Alice's R-b.

Philipp Stanner (3):
  rust: sync: Add abstraction for synchronize_rcu()
  rust: revocable: Use safe synchronize_rcu() abstraction
  rust: sync: Use safe synchronize_rcu() abstraction in poll

 rust/kernel/revocable.rs |  9 ++++++---
 rust/kernel/sync/poll.rs | 10 ++++++----
 rust/kernel/sync/rcu.rs  | 16 ++++++++++++++++
 3 files changed, 28 insertions(+), 7 deletions(-)


base-commit: 43a393185e33e573a374c1d4f7ddf6481484ef8d
-- 
2.54.0

[PATCH v3 1/3] rust: sync: Add abstraction for synchronize_rcu()

[Philipp Stanner]

synchronize_rcu() is a frequently used C function which is always safe
to be called.

Add a safe abstraction for synchronize_rcu().

Signed-off-by: Philipp Stanner <phasta@kernel.org>
Reviewed-by: Onur Özkan <work@onurozkan.dev>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
---
 rust/kernel/sync/rcu.rs | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/rust/kernel/sync/rcu.rs b/rust/kernel/sync/rcu.rs
index a32bef6e490b..2bae76d229f0 100644
--- a/rust/kernel/sync/rcu.rs
+++ b/rust/kernel/sync/rcu.rs
@@ -50,3 +50,19 @@ fn drop(&mut self) {
 pub fn read_lock() -> Guard {
     Guard::new()
 }
+
+/// Wait for one RCU grace period.
+///
+/// Waits for all RCU read-side critical sections (such as those established by
+/// a [`rcu::Guard`]) at the moment of the function call to finish.
+///
+/// Does not prevent new read-side critical sections from starting, which may
+/// begin and run while this call is blocking.
+///
+/// Note that this is one of the RCU primitives which must not be called in
+/// atomic context.
+#[inline]
+pub fn synchronize_rcu() {
+    // SAFETY: `synchronize_rcu()` is always safe to be called from process context.
+    unsafe { bindings::synchronize_rcu() };
+}
-- 
2.54.0

[PATCH v3 2/3] rust: revocable: Use safe synchronize_rcu() abstraction

[Philipp Stanner]

We now have a safe wrapper for the foreign function synchronize_rcu().

Use it in revocable.rs.

Signed-off-by: Philipp Stanner <phasta@kernel.org>
Reviewed-by: Onur Özkan <work@onurozkan.dev>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
---
 rust/kernel/revocable.rs | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/revocable.rs b/rust/kernel/revocable.rs
index 0f4ae673256d..f539603349f1 100644
--- a/rust/kernel/revocable.rs
+++ b/rust/kernel/revocable.rs
@@ -7,7 +7,11 @@
 
 use pin_init::Wrapper;
 
-use crate::{bindings, prelude::*, sync::rcu, types::Opaque};
+use crate::{
+    prelude::*,
+    sync::rcu,
+    types::Opaque, //
+};
 use core::{
     marker::PhantomData,
     ops::Deref,
@@ -161,8 +165,7 @@ unsafe fn revoke_internal<const SYNC: bool>(&self) -> bool {
 
         if revoke {
             if SYNC {
-                // SAFETY: Just an FFI call, there are no further requirements.
-                unsafe { bindings::synchronize_rcu() };
+                rcu::synchronize_rcu();
             }
 
             // SAFETY: We know `self.data` is valid because only one CPU can succeed the
-- 
2.54.0

[PATCH v3 3/3] rust: sync: Use safe synchronize_rcu() abstraction in poll

[Philipp Stanner]

We now have a safe wrapper for the foreign function synchronize_rcu().

Use it in poll.rs.

Signed-off-by: Philipp Stanner <phasta@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Onur Özkan <work@onurozkan.dev>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
---
 rust/kernel/sync/poll.rs | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/rust/kernel/sync/poll.rs b/rust/kernel/sync/poll.rs
index 0ec985d560c8..30ebeea1702f 100644
--- a/rust/kernel/sync/poll.rs
+++ b/rust/kernel/sync/poll.rs
@@ -8,7 +8,11 @@
     bindings,
     fs::File,
     prelude::*,
-    sync::{CondVar, LockClassKey},
+    sync::{
+        CondVar,
+        LockClassKey,
+        rcu::synchronize_rcu, //
+    }, //
 };
 use core::{marker::PhantomData, ops::Deref};
 
@@ -99,8 +103,6 @@ fn drop(self: Pin<&mut Self>) {
         unsafe { bindings::__wake_up_pollfree(self.inner.wait_queue_head.get()) };
 
         // Wait for epoll items to be properly removed.
-        //
-        // SAFETY: Just an FFI call.
-        unsafe { bindings::synchronize_rcu() };
+        synchronize_rcu();
     }
 }
-- 
2.54.0

Re: [PATCH v3 0/3] Add and use abstraction for synchronize_rcu()

[Boqun Feng]

On Wed, Jun 24, 2026 at 05:07:01PM +0200, Philipp Stanner wrote:
> Changes since v2:
>   - Compromise docu for "RCU versus atomic context" a bit better
>   - Add respective R-b's
> 
> Changes since v1:
>   - Vertically format imports. (Onur)
>   - Make the new function #[inline]. (Alice)
>   - Add Alice's R-b.
> 
> Philipp Stanner (3):
>   rust: sync: Add abstraction for synchronize_rcu()
>   rust: revocable: Use safe synchronize_rcu() abstraction
>   rust: sync: Use safe synchronize_rcu() abstraction in poll
> 
>  rust/kernel/revocable.rs |  9 ++++++---
>  rust/kernel/sync/poll.rs | 10 ++++++----
>  rust/kernel/sync/rcu.rs  | 16 ++++++++++++++++
>  3 files changed, 28 insertions(+), 7 deletions(-)
> 

Queue it in rust-sync

	https://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git/ rust-sync

Thank you all!

Regards,
Boqun

> 
> base-commit: 43a393185e33e573a374c1d4f7ddf6481484ef8d
> -- 
> 2.54.0
>