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

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Message-ID: <CAH5fLgguMwp=jfSG=BSDWxCVO7cd2MQVfLsFLH2byDBJVZbOfg@mail.gmail.com>
Date: Fri, 22 Nov 2024 16:53:58 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Miguel Ojeda <ojeda@...nel.org>, Matthew Wilcox <willy@...radead.org>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 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>
Cc: 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 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.

Alice