linux-kernel - Re: [PATCH v9 8/8] task: rust: rework how current is accessed

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Message-ID: <ba35cb10-21e0-493a-935e-f314bc0214c4@lucifer.local>
Date: Fri, 22 Nov 2024 17:34:19 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>, John Hubbard <jhubbard@...dia.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, Christian Brauner <brauner@...nel.org>,
        Jann Horn <jannh@...gle.com>, Suren Baghdasaryan <surenb@...gle.com>,
        Alex Gaynor <alex.gaynor@...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>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, rust-for-linux@...r.kernel.org,
        Andreas Hindborg <a.hindborg@...nel.org>
Subject: Re: [PATCH v9 8/8] task: rust: rework how current is accessed

On Fri, Nov 22, 2024 at 04:53:58PM +0100, Alice Ryhl wrote:
> On Fri, Nov 22, 2024 at 4:41 PM Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > Introduce a new type called `CurrentTask` that lets you perform various
> > operations that are only safe on the `current` task. Use the new type to
> > provide a way to access the current mm without incrementing its
> > refcount.
> >
> > With this change, you can write stuff such as
> >
> >         let vma = current!().mm().lock_vma_under_rcu(addr);
> >
> > without incrementing any refcounts.
> >
> > Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
>
> Oh, that's awkward, I was testing this change using a config file that
> was missing CONFIG_RUST=y, so it didn't compile the code at all. You
> need the following imports for this to work:
>
> diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
> index 103d235eb844..60659076997a 100644
> --- a/rust/kernel/task.rs
> +++ b/rust/kernel/task.rs
> @@ -7,7 +7,8 @@
>  use crate::{
>      bindings,
>      ffi::{c_int, c_long, c_uint},
> -    types::{NotThreadSafe, Opaque},
> +    mm::MmWithUser,
> +    types::Opaque,
>  };
>  use core::{
>      cmp::{Eq, PartialEq},
>
> Otherwise the code should be correct. You can fetch the tree with this fixed at:
> https://github.com/Darksonn/linux/commits/b4/vma/
>
> I'll fix it in the next version, but I will wait for review before I send that.

Sure, no problem, we can just make this a predicate for the ack.

>
> Alice