[PATCH v2 0/3] Add and use abstraction for synchronize_rcu()

[PATCH v2 0/3] Add and use abstraction for synchronize_rcu()

[Philipp Stanner]

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  |  9 +++++++++
 3 files changed, 21 insertions(+), 7 deletions(-)


base-commit: 43a393185e33e573a374c1d4f7ddf6481484ef8d
-- 
2.54.0

[PATCH v2 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>
---
 rust/kernel/sync/rcu.rs | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/rust/kernel/sync/rcu.rs b/rust/kernel/sync/rcu.rs
index a32bef6e490b..0d438ef31766 100644
--- a/rust/kernel/sync/rcu.rs
+++ b/rust/kernel/sync/rcu.rs
@@ -50,3 +50,12 @@ fn drop(&mut self) {
 pub fn read_lock() -> Guard {
     Guard::new()
 }
+
+/// Wait for one RCU grace period.
+///
+/// You typically do this to wait for everyone holding a [`Guard`].
+#[inline]
+pub fn synchronize_rcu() {
+    // SAFETY: `synchronize_rcu()` is always safe to be called. It just waits for a grace period.
+    unsafe { bindings::synchronize_rcu() };
+}
-- 
2.54.0

[PATCH v2 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>
---
 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 v2 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>
---
 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 v2 0/3] Add and use abstraction for synchronize_rcu()

[Onur Özkan]

On Mon, 22 Jun 2026 19:32:48 +0200
Philipp Stanner <phasta@kernel.org> wrote:

> 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  |  9 +++++++++
>  3 files changed, 21 insertions(+), 7 deletions(-)
> 
> 
> base-commit: 43a393185e33e573a374c1d4f7ddf6481484ef8d
> -- 
> 2.54.0
> 

For the whole series:

Reviewed-by: Onur Özkan <work@onurozkan.dev>

Re: [PATCH v2 1/3] rust: sync: Add abstraction for synchronize_rcu()

[Gary Guo]

On Mon Jun 22, 2026 at 6:32 PM BST, Philipp Stanner wrote:
> 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: Gary Guo <gary@garyguo.net>

> ---
>  rust/kernel/sync/rcu.rs | 9 +++++++++
>  1 file changed, 9 insertions(+)

Re: [PATCH v2 2/3] rust: revocable: Use safe synchronize_rcu() abstraction

[Gary Guo]

On Mon Jun 22, 2026 at 6:32 PM BST, Philipp Stanner wrote:
> 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: Gary Guo <gary@garyguo.net>

> ---
>  rust/kernel/revocable.rs | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)

Re: [PATCH v2 3/3] rust: sync: Use safe synchronize_rcu() abstraction in poll

[Gary Guo]

On Mon Jun 22, 2026 at 6:32 PM BST, Philipp Stanner wrote:
> 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: Gary Guo <gary@garyguo.net>

> ---
>  rust/kernel/sync/poll.rs | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)

Re: [PATCH v2 1/3] rust: sync: Add abstraction for synchronize_rcu()

[Danilo Krummrich]

On Mon Jun 22, 2026 at 7:32 PM CEST, Philipp Stanner wrote:
> +/// Wait for one RCU grace period.
> +///
> +/// You typically do this to wait for everyone holding a [`Guard`].

NIT: "typically" reads a bit as if there were other reasons to call
synchronize_rcu() than to wait for all concurrent RCU read side critical
sections.

Also, while it's implicit, it might still be worth to explicitly call out that
this means concurrently held Guard objects (concurrent read side critical
sections), i.e. subsequent read side critical sections may still run
concurrently.

> +#[inline]
> +pub fn synchronize_rcu() {
> +    // SAFETY: `synchronize_rcu()` is always safe to be called. It just waits for a grace period.
> +    unsafe { bindings::synchronize_rcu() };
> +}
> -- 
> 2.54.0

Re: [PATCH v2 0/3] Add and use abstraction for synchronize_rcu()

[Danilo Krummrich]

On Mon Jun 22, 2026 at 7:32 PM CEST, Philipp Stanner wrote:
>   rust: sync: Add abstraction for synchronize_rcu()
>   rust: revocable: Use safe synchronize_rcu() abstraction
>   rust: sync: Use safe synchronize_rcu() abstraction in poll

Reviewed-by: Danilo Krummrich <dakr@kernel.org>