linux-kernel - Re: [PATCH RFC 05/11] rust: sync: Add dummy LockClassKey implementation for !CONFIG

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Date:   Fri, 14 Jul 2023 11:57:58 -0300
From:   Martin Rodriguez Reboredo <yakoyoku@...il.com>
To:     Asahi Lina <lina@...hilina.net>, 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>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>, Tom Rix <trix@...hat.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        asahi@...ts.linux.dev, rust-for-linux@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH RFC 05/11] rust: sync: Add dummy LockClassKey
 implementation for !CONFIG_LOCKDEP

On 7/14/23 06:13, Asahi Lina wrote:
> Lock classes aren't used without lockdep. The C side declares the key
> as an empty struct in that case, but let's make it an explicit ZST in
> Rust, implemented in a separate module. This allows us to more easily
> guarantee that the lockdep code will be trivially optimized out without
> CONFIG_LOCKDEP, including LockClassKey arguments that are passed around.
> 
> Depending on whether CONFIG_LOCKDEP is enabled or not, we then import
> the real lockdep implementation or the dummy one.
> 
> Signed-off-by: Asahi Lina <lina@...hilina.net>
> ---
>   rust/kernel/sync.rs            | 29 ++++++++---------------------
>   rust/kernel/sync/lockdep.rs    | 27 +++++++++++++++++++++++++++
>   rust/kernel/sync/no_lockdep.rs | 19 +++++++++++++++++++
>   3 files changed, 54 insertions(+), 21 deletions(-)
> 
> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
> index d219ee518eff..352472c6b77a 100644
> --- a/rust/kernel/sync.rs
> +++ b/rust/kernel/sync.rs
> @@ -5,37 +5,24 @@
>   //! This module contains the kernel APIs related to synchronisation that have been ported or
>   //! wrapped for usage by Rust code in the kernel.
>   
> -use crate::types::Opaque;
> -
>   mod arc;
>   mod condvar;
>   pub mod lock;
>   mod locked_by;
>   
> +#[cfg(CONFIG_LOCKDEP)]
> +mod lockdep;
> +#[cfg(not(CONFIG_LOCKDEP))]
> +mod no_lockdep;

Some care must be taken wrt how is it going to appear in the resulting
documentation, I think it can lead to missing details. `#[cfg(doc)]`
should be considered.

> +#[cfg(not(CONFIG_LOCKDEP))]
> +use no_lockdep as lockdep;
> [...]