linux-kernel - Re: [PATCH v13 2/6] rust: introduce module

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Message-Id: <DB03MZI2FCOW.2JBFL3TY38FK@kernel.org>
Date: Mon, 30 Jun 2025 21:02:37 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Andreas Hindborg" <a.hindborg@...nel.org>
Cc: "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>, "Alice Ryhl" <aliceryhl@...gle.com>, "Masahiro
 Yamada" <masahiroy@...nel.org>, "Nathan Chancellor" <nathan@...nel.org>,
 "Luis Chamberlain" <mcgrof@...nel.org>, "Danilo Krummrich"
 <dakr@...nel.org>, "Nicolas Schier" <nicolas.schier@...ux.dev>, "Trevor
 Gross" <tmgross@...ch.edu>, "Adam Bratschi-Kaye" <ark.email@...il.com>,
 <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-kbuild@...r.kernel.org>, "Petr Pavlu" <petr.pavlu@...e.com>, "Sami
 Tolvanen" <samitolvanen@...gle.com>, "Daniel Gomez" <da.gomez@...sung.com>,
 "Simona Vetter" <simona.vetter@...ll.ch>, "Greg KH"
 <gregkh@...uxfoundation.org>, "Fiona Behrens" <me@...enk.dev>, "Daniel
 Almeida" <daniel.almeida@...labora.com>, <linux-modules@...r.kernel.org>
Subject: Re: [PATCH v13 2/6] rust: introduce module_param module

On Mon Jun 30, 2025 at 3:15 PM CEST, Andreas Hindborg wrote:
> "Benno Lossin" <lossin@...nel.org> writes:
>> On Mon Jun 30, 2025 at 1:18 PM CEST, Andreas Hindborg wrote:
>>> "Benno Lossin" <lossin@...nel.org> writes:
>>>> (no idea if the orderings are correct, I always have to think way to
>>>> much about that... especially since our atomics seem to only take one
>>>> ordering in compare_exchange?)
>>>>
>>>>> As far as I can tell, atomics may not land in v6.17, so this series
>>>>> will probably not be ready for merge until v6.18 at the earliest.
>>>>
>>>> Yeah, sorry about that :(
>>>
>>> Actually, perhaps we could aim at merging this code without this
>>> synchronization?
>>
>> I won't remember this issue in a few weeks and I fear that it will just
>> get buried. In fact, I already had to re-read now what the actual issue
>> was...
>>
>>> The lack of synchronization is only a problem if we
>>> support custom parsing. This patch set does not allow custom parsing
>>> code, so it does not suffer this issue.
>>
>> ... In doing that, I saw my original example of UB:
>>
>>     module! {
>>         // ...
>>         params: {
>>             my_param: i64 {
>>                 default: 0,
>>                 description: "",
>>             },
>>         },
>>     }
>>
>>     static BAD: &'static i64 = module_parameters::my_param.get();
>>
>> That can happen without custom parsing, so it's still a problem...
>
> Ah, got it. Thanks.

On second thought, we *could* just make the accessor function `unsafe`.
Of course with a pinky promise to make the implementation safe once
atomics land. But I think if it helps you get your driver faster along,
then we should do it.

---
Cheers,
Benno