Re: [PATCH v3 06/16] rust: add rcu abstraction

[Alice Ryhl]

On Tue, Oct 22, 2024 at 11:33 PM Danilo Krummrich <dakr@xxxxxxxxxx> wrote:
>
> From: Wedson Almeida Filho <wedsonaf@xxxxxxxxx>
>
> Add a simple abstraction to guard critical code sections with an rcu
> read lock.
>
> Signed-off-by: Wedson Almeida Filho <wedsonaf@xxxxxxxxx>
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>

Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>

>  rust/helpers/helpers.c  |  1 +
>  rust/helpers/rcu.c      | 13 +++++++++++
>  rust/kernel/sync.rs     |  1 +
>  rust/kernel/sync/rcu.rs | 52 +++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 67 insertions(+)
>  create mode 100644 rust/helpers/rcu.c
>  create mode 100644 rust/kernel/sync/rcu.rs
>
> diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
> index 20a0c69d5cc7..0720debccdd4 100644
> --- a/rust/helpers/helpers.c
> +++ b/rust/helpers/helpers.c
> @@ -16,6 +16,7 @@
>  #include "mutex.c"
>  #include "page.c"
>  #include "rbtree.c"
> +#include "rcu.c"
>  #include "refcount.c"
>  #include "signal.c"
>  #include "slab.c"
> diff --git a/rust/helpers/rcu.c b/rust/helpers/rcu.c
> new file mode 100644
> index 000000000000..f1cec6583513
> --- /dev/null
> +++ b/rust/helpers/rcu.c
> @@ -0,0 +1,13 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/rcupdate.h>
> +
> +void rust_helper_rcu_read_lock(void)
> +{
> +       rcu_read_lock();
> +}
> +
> +void rust_helper_rcu_read_unlock(void)
> +{
> +       rcu_read_unlock();
> +}
> 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 ()>,

Once 6.13 is released, you'll want to use NotThreadSafe here instead
of PhantomData. It's landing upstream through vfs.rust.file.

Alice