linux-kernel - Re: [PATCH 1/2] rust: Add initial cpumask abstractions

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Message-ID: <CAH5fLggyEXyyaFNnmBCPOSX051TiFyAp0B8GfahbPg=+LrtUWA@mail.gmail.com>
Date: Tue, 25 Feb 2025 18:12:35 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: Yury Norov <yury.norov@...il.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, 
	Miguel Ojeda <ojeda@...nel.org>, 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>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, linux-kernel@...r.kernel.org, 
	Danilo Krummrich <dakr@...hat.com>, rust-for-linux@...r.kernel.org, 
	Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH 1/2] rust: Add initial cpumask abstractions

On Tue, Feb 25, 2025 at 6:02 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On Tue, 25 Feb 2025 at 17:23, Alice Ryhl <aliceryhl@...gle.com> wrote:
>
> > Is it a problem if a value of type struct cpumask is moved? It looks
> > like it is just an array of longs?
>
> With the current code, if I replace the Box with an on-stack variable,
> the kernel crashes.
>
> In my usecase, the pointer to the cpumask array is sent to the OPP
> core, which may update the content, though it doesn't save the pointer.
>
> But for another usecase, the C code may end up saving the pointer.

I don't think that case applies here. Variables that could be stashed
like that need a destructor that removes the pointer from the relevant
C structures. This is because pinning only prevents the owner from
moving the variable - it doesn't prevent the owner from destroying it.

Alice