[PATCH v2 1/3] arm64: Fix non-atomic __READ_ONCE() with CONFIG_LTO=y

[Marco Elver]

On Thu, 29 Jan 2026 at 02:21, Boqun Feng <boqun at kernel.org> wrote:
>
> On Thu, Jan 29, 2026 at 01:52:32AM +0100, Marco Elver wrote:
> > The implementation of __READ_ONCE() under CONFIG_LTO=y incorrectly
> > qualified the fallback "once" access for types larger than 8 bytes,
> > which are not atomic but should still happen "once" and suppress common
> > compiler optimizations.
> >
> > The cast `volatile typeof(__x)` applied the volatile qualifier to the
> > pointer type itself rather than the pointee. This created a volatile
> > pointer to a non-volatile type, which violated __READ_ONCE() semantics.
> >
> > Fix this by casting to `volatile typeof(*__x) *`.
>
> I guess a `volatile typeof(x) *` also works. Either way, good catch!

x might expand to some big expression, so better to refer to it only
once, and then use the same-typed *__x as a proxy. Semantically the
same, but compile-times ought to be better this way.

> Reviewed-by: Boqun Feng <boqun at kernel.org>

Thanks!