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: <877c0joyfo.fsf@kernel.org>
Date: Tue, 08 Jul 2025 10:54:03 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>
Cc: "Alice Ryhl" <aliceryhl@...gle.com>,  "Miguel Ojeda" <ojeda@...nel.org>,
  "Alex Gaynor" <alex.gaynor@...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`

"Boqun Feng" <boqun.feng@...il.com> writes:

> On Mon, Jul 07, 2025 at 03:38:58PM +0200, Alice Ryhl wrote:
>> 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, I think we can do the similar as Revocable here:
>
>         if *self.init.get_mut() == 2 { }
>
> Further, with my following Benno's suggestion and making `Atomic<T>` an
> `UnsafeCell<T>:
>
> 	https://lore.kernel.org/rust-for-linux/aGhh-TvNOWhkt0JG@Mac.home/
>
> compiler can generate a noalias reference here, which allows further
> optimization.
>

You would like to remove `PhantomPinned` to enable noalias? I guess that
makes sense in this case. I'll fix that for next spin.


Best regards,
Andreas Hindborg