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Message-ID: <CALNs47vWo1Ae2PJ+80xm1eB057DDsF+SbmVun-UHc9+vzpr7nQ@mail.gmail.com>
Date: Mon, 5 Feb 2024 21:14:15 -0500
From: Trevor Gross <tmgross@...ch.edu>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
Wedson Almeida Filho <wedsonaf@...il.com>, Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...sung.com>,
Peter Zijlstra <peterz@...radead.org>, Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Arve Hjønnevåg <arve@...roid.com>,
Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>,
Joel Fernandes <joel@...lfernandes.org>, Carlos Llamas <cmllamas@...gle.com>,
Suren Baghdasaryan <surenb@...gle.com>, Dan Williams <dan.j.williams@...el.com>,
Kees Cook <keescook@...omium.org>, Matthew Wilcox <willy@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>, Daniel Xu <dxu@...uu.xyz>, linux-kernel@...r.kernel.org,
rust-for-linux@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v4 1/9] rust: types: add `NotThreadSafe`
On Fri, Feb 2, 2024 at 5:56 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
>
> This introduces a new marker type for types that shouldn't be thread
> safe. By adding a field of this type to a struct, it becomes non-Send
> and non-Sync, which means that it cannot be accessed in any way from
> threads other than the one it was created on.
>
> This is useful for APIs that require globals such as `current` to remain
> constant while the value exists.
>
> We update two existing users in the Kernel to use this helper:
>
> * `Task::current()` - moving the return type of this value to a
> different thread would not be safe as you can no longer be guaranteed
> that the `current` pointer remains valid.
> * Lock guards. Mutexes and spinlocks should be unlocked on the same
> thread as where they were locked, so we enforce this using the Send
> trait.
>
> There are also additional users in later patches of this patchset. See
> [1] and [2] for the discussion that led to the introducion of this
s/introducion/introduction
> patch.
>
> Link: https://lore.kernel.org/all/nFDPJFnzE9Q5cqY7FwSMByRH2OAn_BpI4H53NQfWIlN6I2qfmAqnkp2wRqn0XjMO65OyZY4h6P4K2nAGKJpAOSzksYXaiAK_FoH_8QbgBI4=@proton.me/ [1]
> Link: https://lore.kernel.org/all/nFDPJFnzE9Q5cqY7FwSMByRH2OAn_BpI4H53NQfWIlN6I2qfmAqnkp2wRqn0XjMO65OyZY4h6P4K2nAGKJpAOSzksYXaiAK_FoH_8QbgBI4=@proton.me/ [2]
> Suggested-by: Benno Lossin <benno.lossin@...ton.me>
> Reviewed-by: Benno Lossin <benno.lossin@...ton.me>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
> rust/kernel/sync/lock.rs | 15 +++++++++++----
> rust/kernel/task.rs | 10 ++++++----
> rust/kernel/types.rs | 17 +++++++++++++++++
> 3 files changed, 34 insertions(+), 8 deletions(-)
>
> diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
> index 149a5259d431..d08d9d32915a 100644
> --- a/rust/kernel/sync/lock.rs
> +++ b/rust/kernel/sync/lock.rs
> @@ -6,8 +6,15 @@
> //! spinlocks, raw spinlocks) to be provided with minimal effort.
>
> use super::LockClassKey;
> -use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque, types::ScopeGuard};
> -use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned};
> +use crate::{
> + bindings,
> + init::PinInit,
> + pin_init,
> + str::CStr,
> + types::ScopeGuard,
> + types::{NotThreadSafe, Opaque},
Formatting nit: ScopeGuard could probably be placed in the same group
as NotThreadSafe & Opaque
> [...]
> +
> +/// Zero-sized type to mark types not [`Send`].
> +///
> +/// Add this type as a field to your struct if your type should not be sent to a different task.
> +/// Since [`Send`] is an auto trait, adding a single field that is `!Send` will ensure that the
> +/// whole type is `!Send`.
> +///
> +/// If a type is `!Send` it is impossible to give control over an instance of the type to another
> +/// task. This is useful when a type stores task-local information for example file descriptors.
I initially read this thinking it meant to include this type if your
struct also had a FD rather than being part of the FD. Maybe
This is useful to include in types that store or reference task-local
information. A file descriptor is an example of one such type.
> +pub type NotThreadSafe = PhantomData<*mut ()>;
> +
> +/// Used to construct instances of type [`NotThreadSafe`] similar to how we construct
> +/// `PhantomData`.
I think it sounds slightly better reworded from personal to passive, i.e.
... similar to how `PhantomData` is constructed.
> +/// [`NotThreadSafe`]: type@...ThreadSafe
> +#[allow(non_upper_case_globals)]
> +pub const NotThreadSafe: NotThreadSafe = PhantomData;
> --
> 2.43.0.594.gd9cf4e227d-goog
This looks good, sounds nice to make the intent more clear. Nothing
that isn't optional, so
Reviewed-by: Trevor Gross <tmgross@...ch.edu>
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