linux-kernel - Re: [PATCH 4/7] rust: init: wrap type checking struct initializers in a closure

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Message-ID: <Cs0WvAGhcBydk2RmwKLuog68EzhWu-Uc6ZTUrXBs7vgUozT07W9JebR0KiFQokDpWVGkotW68iEzW9TYFym5jDvpGMp5AqlpSsmLUUDgeNE=@proton.me>
Date:   Sat, 24 Jun 2023 21:05:28 +0000
From:   Benno Lossin <benno.lossin@...ton.me>
To:     Björn Roy Baron <bjorn3_gh@...tonmail.com>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Andreas Hindborg <nmi@...aspace.dk>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev
Subject: Re: [PATCH 4/7] rust: init: wrap type checking struct initializers in a closure

On 6/24/23 17:03, Björn Roy Baron wrote:
> On Saturday, June 24th, 2023 at 11:25, Benno Lossin <benno.lossin@...ton.me> wrote:
> 
>> In the implementation of the init macros there is a `if false` statement
>> that type checks the initializer to ensure every field is initialized.
>> Since the next patch has a stack variable to store the struct, the
>> function might allocate too much memory on debug builds. Putting the
>> struct into a closure ensures that even in debug builds no stack
>> overflow error is caused. In release builds this was not a problem since
>> the code was optimized away due to the `if false`.
>>
>> Signed-off-by: Benno Lossin <benno.lossin@...ton.me>
>> ---
>>   rust/kernel/init/macros.rs | 18 +++++++++++-------
>>   1 file changed, 11 insertions(+), 7 deletions(-)
>>
>> diff --git a/rust/kernel/init/macros.rs b/rust/kernel/init/macros.rs
>> index df4281743175..1e0c4aca055a 100644
>> --- a/rust/kernel/init/macros.rs
>> +++ b/rust/kernel/init/macros.rs
>> @@ -1037,14 +1037,18 @@ macro_rules! __init_internal {
>>                       // We use unreachable code to ensure that all fields have been mentioned exactly
>>                       // once, this struct initializer will still be type-checked and complain with a
>>                       // very natural error message if a field is forgotten/mentioned more than once.
>> -                    #[allow(unreachable_code, clippy::diverging_sub_expression)]
>> +                    #[allow(unreachable_code,
>> +                            clippy::diverging_sub_expression,
>> +                            clippy::redundant_closure_call)]
>>                       if false {
>> -                        $crate::__init_internal!(make_initializer:
>> -                            @slot(slot),
>> -                            @type_name($t),
>> -                            @munch_fields($($fields)*,),
>> -                            @acc(),
>> -                        );
>> +                        (|| {
>> +                            $crate::__init_internal!(make_initializer:
>> +                                @slot(slot),
>> +                                @type_name($t),
>> +                                @munch_fields($($fields)*,),
>> +                                @acc(),
>> +                            );
>> +                        })();
> 
> Is it necessary to call this closure? Typechecking of the closure should happen even without calling it.

You are right, I do not need to call it. Will fix.

-- 
Cheers,
Benno

> 
>>                       }
>>                   }
>>                   Ok(__InitOk)
>> --
>> 2.41.0
> 
> Cheers,
> Björn