[PATCH v2 04/10] rust: add rcu abstraction

Danilo Krummrich
2024-06-18T23:41:01Z

From: Wedson Almeida Filho <wedsonaf@gmail.com>

Add a simple abstraction to guard critical code sections with an rcu
read lock.

Co-developed-by: Andreas Hindborg <a.hindborg@samsung.com>
Signed-off-by: Andreas Hindborg <a.hindborg@samsung.com>
Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
---
rust/helpers.c | 15 ++++++++++++
rust/kernel/sync.rs | 1 +
rust/kernel/sync/rcu.rs | 52 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 68 insertions(+)
create mode 100644 rust/kernel/sync/rcu.rs

diff --git a/rust/helpers.c b/rust/helpers.c
index 0e02b2c64c72..0ce40ccb978b 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -27,6 +27,7 @@
#include <linux/err.h>
#include <linux/errname.h>
#include <linux/mutex.h>
+#include <linux/rcupdate.h>
#include <linux/refcount.h>
#include <linux/sched/signal.h>
#include <linux/slab.h>
@@ -166,6 +167,20 @@ rust_helper_krealloc(const void *objp, size_t new_size, gfp_t flags)
}
EXPORT_SYMBOL_GPL(rust_helper_krealloc);

+/* rcu */
+void rust_helper_rcu_read_lock(void)
+{
+ rcu_read_lock();
+}
+EXPORT_SYMBOL_GPL(rust_helper_rcu_read_lock);
+
+void rust_helper_rcu_read_unlock(void)
+{
+ rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(rust_helper_rcu_read_unlock);
+/* end rcu */
+
/*
* `bindgen` binds the C `size_t` type as the Rust `usize` type, so we can
* use it in contexts where Rust expects a `usize` like slice (array) indices.
diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index 0ab20975a3b5..1806767359fe 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -11,6 +11,7 @@
mod condvar;
pub mod lock;
mod locked_by;
+pub mod rcu;

pub use arc::{Arc, ArcBorrow, UniqueArc};
pub use condvar::{new_condvar, CondVar, CondVarTimeoutResult};
diff --git a/rust/kernel/sync/rcu.rs b/rust/kernel/sync/rcu.rs
new file mode 100644
index 000000000000..5a35495f69a4
--- /dev/null
+++ b/rust/kernel/sync/rcu.rs
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! RCU support.
+//!
+//! C header: [`include/linux/rcupdate.h`](srctree/include/linux/rcupdate.h)
+
+use crate::bindings;
+use core::marker::PhantomData;
+
+/// Evidence that the RCU read side lock is held on the current thread/CPU.
+///
+/// The type is explicitly not `Send` because this property is per-thread/CPU.
+///
+/// # Invariants
+///
+/// The RCU read side lock is actually held while instances of this guard exist.
+pub struct Guard {
+ _not_send: PhantomData<*mut ()>,
+}
+
+impl Guard {
+ /// Acquires the RCU read side lock and returns a guard.
+ pub fn new() -> Self {
+ // SAFETY: An FFI call with no additional requirements.
+ unsafe { bindings::rcu_read_lock() };
+ // INVARIANT: The RCU read side lock was just acquired above.
+ Self {
+ _not_send: PhantomData,
+ }
+ }
+
+ /// Explicitly releases the RCU read side lock.
+ pub fn unlock(self) {}
+}
+
+impl Default for Guard {
+ fn default() -> Self {
+ Self::new()
+ }
+}
+
+impl Drop for Guard {
+ fn drop(&mut self) {
+ // SAFETY: By the type invariants, the rcu read side is locked, so it is ok to unlock it.
+ unsafe { bindings::rcu_read_unlock() };
+ }
+}
+
+/// Acquires the RCU read side lock.
+pub fn read_lock() -> Guard {
+ Guard::new()
+}
--
2.45.1