Re: [PATCH 1/1] rust: sync: Make `GlobalLockedBy::as_ref` unavailable if T is not Sync

[Boqun Feng <boqun@kernel.org>]

On Mon, Oct 19, 2026 at 09:49:22AM +0200, Alice Ryhl wrote:
> On Fri, Oct 16, 2026 at 7:19 PM Priya Bala Govindasamy <pgovind2@uci.edu> wrote:
> >
> > The `GlobalLockedBy::as_ref` method allows `&T` to be obtained from
> > mutliple threads even if `T` is not Sync.
> >
> > This happens because `GlobalLockedBy<T, B>` is Sync if
> > `LockedBy<T, B::item>` is Sync. `LockedBy<T, B>` is Sync if `T` is Send.
> > Since there is no requirement that `T` also implements Sync, it is
> > possible for multiple threads to simultaneously obtain references to a
> > `GlobalLockedBy<T, B>` and then acquire `&T` through
> > `GlobalLockedBy::as_ref`. This can lead to undefined behavior if `T` does
> > not implement Sync.
> >
> > Note that a reference to `GlobalGuard<B>` is required as an argument to
> > `GlobalLockedBy::as_ref`. Therefore, this issue requires that
> > `GlobalGuard<B>` is `Sync` which happens if `B::item` is `Sync`
> > (for example, ()).
> >
> > Fix this by adding a trait bound to `GlobalLockedBy::as_ref` requiring
> > `T: Sync`.
> >
> > Fixes: 8eea62ff94f4 ("rust: sync: add global lock support")
> > Reported-by: Dylan Zueck <dzueck@uci.edu>
> > Assisted-by: LLM
> > Signed-off-by: Priya Bala Govindasamy <pgovind2@uci.edu>
> 
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>

Queued for more review and testing.

Thank you both!

Regards,
Boqun