On Thu, 29 Jan 2026 at 02:21, Boqun Feng [off-list ref] wrote:

On Thu, Jan 29, 2026 at 01:52:32AM +0100, Marco Elver wrote:

quoted

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@kernel.org>

Thanks!