Re: [RFC v2 PATCH] futex: extend set_robust_list to allow 2 locking ABIs at the same time.

Thomas Gleixner
2019-11-05T09:59:32Z

On Tue, 5 Nov 2019, Florian Weimer wrote:
> * Shawn Landden:
> > If this new ABI is used, then bit 1 of the *next pointer of the
> > user-space robust_list indicates that the futex_offset2 value should
> > be used in place of the existing futex_offset.
>
> The futex interface currently has some races which can only be fixed by
> API changes. I'm concerned that we sacrifice the last bit for some
> rather obscure feature. What if we need that bit for fixing the
> correctness issues?

That current approach is going nowhere and if we change the ABI ever then
this needs to happen with all *libc folks involved and agreeing.

Out of curiosity, what's the race issue vs. robust list which you are
trying to solve?

Thanks,

tglx