linux-kernel - Re: [PATCH v15 1/7] rust: sync: add `SetOnce`

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: <87cyaboypx.fsf@kernel.org>
Date: Tue, 08 Jul 2025 10:47:54 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Alice Ryhl" <aliceryhl@...gle.com>
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>,
  "Masahiro Yamada" <masahiroy@...nel.org>,  "Nathan Chancellor"
 <nathan@...nel.org>,  "Luis Chamberlain" <mcgrof@...nel.org>,  "Danilo
 Krummrich" <dakr@...nel.org>,  "Benno Lossin" <lossin@...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 v15 1/7] rust: sync: add `SetOnce`

"Alice Ryhl" <aliceryhl@...gle.com> writes:

> On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
>>
>> Introduce the `SetOnce` type, a container that can only be written once.
>> The container uses an internal atomic to synchronize writes to the internal
>> value.
>>
>> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
>
> LGTM:
> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
>
>> +impl<T> Drop for SetOnce<T> {
>> +    fn drop(&mut self) {
>> +        if self.init.load(Acquire) == 2 {
>> +            // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value`
>> +            // contains a valid value. We have exclusive access, as we hold a `mut` reference to
>> +            // `self`.
>> +            unsafe { drop_in_place(self.value.get()) };
>
> This load does not need to be Acquire. It can be a Relaxed load or
> even an unsynchronized one since the access is exclusive.

Right, that is actually very cool. My rationale was that if a reference
has been shared to another thread of execution, we would need to
synchronize here to see a possible initialization from that other
thread. But I guess it is impossible to end the lifetime of a reference
without doing a synchronization somewhere else.


Best regards,
Andreas Hindborg