Re: Futex hash_bucket lock can break isolation and cause priority inversion on RT

Peter Zijlstra
2024-10-09T07:22:21Z

On Tue, Oct 08, 2024 at 03:44:23PM -0400, Waiman Long wrote:
>
> On 10/8/24 1:38 PM, Peter Zijlstra wrote:
> > On Tue, Oct 08, 2024 at 04:22:26PM +0100, Juri Lelli wrote:
> > > Does this report make any sense? If it does, has this issue ever been
> > > reported and possibly discussed? I guess it’s kind of a corner case, but
> > > I wonder if anybody has suggestions already on how to possibly try to
> > > tackle it from a kernel perspective.
> > Any shared lock can cause such havoc. Futex hash buckets is just one of
> > a number of very popular ones that's relatively easy to hit.
> >
> > I do have some futex-numa patches still pending, but they won't
> > magically sure this either. Userspace needs help at the very least.
>
> Regarding the futex-numa patches, are you planning to get them merged soon?
> We have customers asking for that.

They're on the todo list somewhere... I know Ampere had interest, other
than that nobody really said anything.