[RFC PATCH] lib: Introduce generic __cmpxchg_u64() and use it where needed

[Peter Zijlstra]

On Thu, Nov 01, 2018 at 09:59:38AM -0700, Eric Dumazet wrote:
> On 11/01/2018 09:32 AM, Peter Zijlstra wrote:
> 
> >> Anyhow, if the atomic maintainers are willing to stand up and state for
> >> the record that the atomic counters are guaranteed to wrap modulo 2^n
> >> just like unsigned integers, then I'm happy to take Paul's patch.
> > 
> > I myself am certainly relying on it.
> 
> Could we get uatomic_t support maybe ?

Whatever for; it'd be the exact identical same functions as for
atomic_t, except for a giant amount of code duplication to deal with the
new type.

That is; today we merged a bunch of scripts that generates most of
atomic*_t, so we could probably script uatomic*_t wrappers with minimal
effort, but it would add several thousand lines of code to each compile
for absolutely no reason what so ever.

> This reminds me of this sooooo silly patch :/
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=adb03115f4590baa280ddc440a8eff08a6be0cb7

Yes, that's stupid. UBSAN is just wrong there.