On Mon, Dec 6, 2021 at 3:28 PM Kees Cook [off-list ref] wrote:

I'm not arguing for refcount_t -- I'm arguing for an API that isn't a
regression of features that have been protecting the kernel from bugs.

Maybe somebody could actually just fix refcount_t instead. Somebody
who cares about that currently horrendously bad interface.

Fix it to not do the fundamentally broken saturation that actively
destroys state: fix it to have a safe "try to increment", instead of
an unsafe "increment and do bad things".

Fix it to not unnecessarily use expensive compare-and-exchange loops,
when you can safely just race a bit, safe in the knowledge that you're
not going to race 2**31 times.

IOW, I think that "try_get_page()" function is basically the *much*
superior version of what is currently a broken "refcount_inc()".

And yes, it does warn about that overflow case that you claim only
refcount_t does. And does so without the broken semantics that
refcount h as.

                Linus