linux-kernel - Re: [PATCH v5 04/26] rust: alloc: implement `Allocator` for `Kmalloc`

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Message-ID: <CAH5fLgjNfJyyZygWzeTyrNi8TQNAquufxFxDgJHzq6dan=b9BQ@mail.gmail.com>
Date: Wed, 14 Aug 2024 15:50:27 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: ojeda@...nel.org, alex.gaynor@...il.com, wedsonaf@...il.com, 
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	benno.lossin@...ton.me, a.hindborg@...sung.com, akpm@...ux-foundation.org, 
	daniel.almeida@...labora.com, faith.ekstrand@...labora.com, 
	boris.brezillon@...labora.com, lina@...hilina.net, mcanal@...lia.com, 
	zhiw@...dia.com, cjia@...dia.com, jhubbard@...dia.com, airlied@...hat.com, 
	ajanulgu@...hat.com, lyude@...hat.com, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v5 04/26] rust: alloc: implement `Allocator` for `Kmalloc`

On Wed, Aug 14, 2024 at 3:48 PM Danilo Krummrich <dakr@...nel.org> wrote:
>
> On Wed, Aug 14, 2024 at 03:44:56PM +0200, Alice Ryhl wrote:
> > On Wed, Aug 14, 2024 at 3:36 PM Danilo Krummrich <dakr@...nel.org> wrote:
> > >
> > > On Wed, Aug 14, 2024 at 09:51:34AM +0200, Alice Ryhl wrote:
> > > > On Mon, Aug 12, 2024 at 8:24 PM Danilo Krummrich <dakr@...nel.org> wrote:
> > > > >
> > > > > Implement `Allocator` for `Kmalloc`, the kernel's default allocator,
> > > > > typically used for objects smaller than page size.
> > > > >
> > > > > All memory allocations made with `Kmalloc` end up in `krealloc()`.
> > > > >
> > > > > It serves as allocator for the subsequently introduced types `KBox` and
> > > > > `KVec`.
> > > > >
> > > > > Signed-off-by: Danilo Krummrich <dakr@...nel.org>
> > > > > ---
> > > > >  rust/helpers.c                 |  3 +-
> > > > >  rust/kernel/alloc.rs           |  2 +-
> > > > >  rust/kernel/alloc/allocator.rs | 63 +++++++++++++++++++++++++++++++++-
> > > > >  3 files changed, 64 insertions(+), 4 deletions(-)
> > > > >
> > > > > diff --git a/rust/helpers.c b/rust/helpers.c
> > > > > index 92d3c03ae1bd..9f7275493365 100644
> > > > > --- a/rust/helpers.c
> > > > > +++ b/rust/helpers.c
> > > > > @@ -193,8 +193,7 @@ void rust_helper_init_work_with_key(struct work_struct *work, work_func_t func,
> > > > >  }
> > > > >  EXPORT_SYMBOL_GPL(rust_helper_init_work_with_key);
> > > > >
> > > > > -void * __must_check __realloc_size(2)
> > > > > -rust_helper_krealloc(const void *objp, size_t new_size, gfp_t flags)
> > > > > +void *rust_helper_krealloc(const void *objp, size_t new_size, gfp_t flags)
> > > > >  {
> > > > >         return krealloc(objp, new_size, flags);
> > > > >  }
> > > >
> > > > Why are the various annotations on this helper being removed?
> > >
> > > rust_helper_krealloc() is only called from Rust, hence neither __must_check nor
> > > __realloc_size() should have any effect.
> > >
> > > I also do not apply them in subsequent commits for the vrealloc() and
> > > kvrealloc() helpers for this reason and removed them here for consistency.
> > >
> > > > This deserves an explanation in the commit message.
> > >
> > > I can also add a separate commit for that.
> >
> > I think your change would be more obviously correct if you keep them.
>
> As in generally, or just for this patch?
>
> Generally, I don't think we should indicate compiler checks that actually are
> never done.
>
> For this patch, yes, it's probably better to separate it.

In general. If you keep it, then I don't have to think about whether
it affects bindgen's output. That's the main reason.

Alice