Re: [RFC PATCH] futex: Introduce __vdso_robust_futex_unlock

[Mathieu Desnoyers]

On 2026-03-13 09:29, Sebastian Andrzej Siewior wrote:
> On 2026-03-13 08:17:57 [-0400], Mathieu Desnoyers wrote:
> > and here we are.
>
> I would still prefer a "small" solution which is expensive in the
> unlikely case if it has to be.

I'm not sure I would call the new robust futex destroy hook solution
"small". Also, I don't think it would be sufficient to fix the robust
PI futex races (my approach handles this as well, see follow up
patches).

> Your vdso version includes asm code which needs to be implemented by
> every architecture.

Correct.

> The exception table did not look like something that
> universally available.

Indeed, we'd need to port the vDSO exception table code from x86 to
other archs.

> Also, if we take this seriously it needs to be
> backported to every stable kernel.

Yes. The same can be said about the hypothetical robust futex destroy
hook.

That being said, I do not expect any "easy" fix for a design
bug that's been unsolved for 16+ years.

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com