linux-kernel - Re: [RFC PATCH 0/3] gpu: nova-core: add basic timer subdevice implementation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Z7xg8uArPlr2gQBU@pollux>
Date: Mon, 24 Feb 2025 13:07:14 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Alexandre Courbot <acourbot@...dia.com>
Cc: Dave Airlie <airlied@...il.com>, Gary Guo <gary@...yguo.net>,
	Joel Fernandes <joel@...lfernandes.org>,
	Boqun Feng <boqun.feng@...il.com>,
	John Hubbard <jhubbard@...dia.com>, Ben Skeggs <bskeggs@...dia.com>,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	nouveau@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [RFC PATCH 0/3] gpu: nova-core: add basic timer subdevice
 implementation

CC: Gary

On Mon, Feb 24, 2025 at 10:40:00AM +0900, Alexandre Courbot wrote:
> This inability to sleep while we are accessing registers seems very
> constraining to me, if not dangerous. It is pretty common to have
> functions intermingle hardware accesses with other operations that might
> sleep, and this constraint means that in such cases the caller would
> need to perform guard lifetime management manually:
> 
>   let bar_guard = bar.try_access()?;
>   /* do something non-sleeping with bar_guard */
>   drop(bar_guard);
> 
>   /* do something that might sleep */
> 
>   let bar_guard = bar.try_access()?;
>   /* do something non-sleeping with bar_guard */
>   drop(bar_guard);
> 
>   ...
> 
> Failure to drop the guard potentially introduces a race condition, which
> will receive no compile-time warning and potentialy not even a runtime
> one unless lockdep is enabled. This problem does not exist with the
> equivalent C code AFAICT, which makes the Rust version actually more
> error-prone and dangerous, the opposite of what we are trying to achieve
> with Rust. Or am I missing something?

Generally you are right, but you have to see it from a different perspective.

What you describe is not an issue that comes from the design of the API, but is
a limitation of Rust in the kernel. People are aware of the issue and with klint
[1] there are solutions for that in the pipeline, see also [2] and [3].

[1] https://rust-for-linux.com/klint
[2] https://github.com/Rust-for-Linux/klint/blob/trunk/doc/atomic_context.md
[3] https://www.memorysafety.org/blog/gary-guo-klint-rust-tools/