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Message-ID: <eea05d26-653e-9cf7-57ce-c5f725e8d6d1@gmail.com>
Date:   Fri, 14 Jul 2023 11:57:58 -0300
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Subject: Re: [PATCH RFC 05/11] rust: sync: Add dummy LockClassKey
 implementation for !CONFIG_LOCKDEP
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To:     Asahi Lina <lina@asahilina.net>, Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?UTF-8?Q?Bj=c3=b6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        Benno Lossin <benno.lossin@proton.me>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nicolas Schier <nicolas@fjasle.eu>, Tom Rix <trix@redhat.com>,
        Daniel Vetter <daniel@ffwll.ch>
Cc:     Hector Martin <marcan@marcan.st>, Sven Peter <sven@svenpeter.dev>,
        Alyssa Rosenzweig <alyssa@rosenzweig.io>,
        asahi@lists.linux.dev, rust-for-linux@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
        llvm@lists.linux.dev
References: <20230714-classless_lockdep-v1-0-229b9671ce31@asahilina.net>
 <20230714-classless_lockdep-v1-5-229b9671ce31@asahilina.net>
From:   Martin Rodriguez Reboredo <yakoyoku@gmail.com>
In-Reply-To: <20230714-classless_lockdep-v1-5-229b9671ce31@asahilina.net>
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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@asahilina.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;
> [...]