On Sun, 15 Feb 2026 at 14:44, Marco Elver [off-list ref] wrote:

I found e.g. xen_get_runstate_snapshot_cpu_delta() uses the >8 byte
case via __READ_ONCE(). READ_ONCE() itself is already restricted to <=
8 bytes (due to that static assert), but that itself uses the
__READ_ONCE() helper which these patches were touching.

I think we could just make __READ_ONCE() be totally unchecked - just
make it be "const volatile typeof()" and leave it at that.

Anybody who uses __READ_ONCE() would then have to deal with it.

There are very few users of that left, I think it's mainly
arch_atomic_read(), which just doesn't want any of the checking that a
regular "READ_ONCE()" does.

In fact, there are *so* few users left that I think we could probably
just remove __READ_ONCE() entirely, and make our "atomic_t" use
"volatile" in the type itself.

I generally absolutely hate volatile on data structures - it's a
design mistake (an understandable one: it was at least partly designed
for memory mapped IO accesses), and the volatile should be in the
accesses, not the data, because very often the volatility of the data
depends on context, not on the data.

But our "atomic_t" is already properly wrapped, and nobody should be
accessing it with anything but our helpers, so putting the volatile
there looks ok.

             Linus