Re: [PATCH] futex: Set USER_DS for the futex_detect_cmpxchg() test

Thomas Gleixner
2018-09-28T06:24:44Z

On Fri, 28 Sep 2018, Thomas Gleixner wrote:

> On Thu, 27 Sep 2018, Andy Lutomirski wrote:
> > I have a couple questions here:
> >
> > - Is this actually okay on all architectures? That is, are there
> > cases where we'll screw up if we fail a USER_DS access this early?
> > s390 stands out as the obvious special case (where USER_DS is not
> > than just a subset of KERNEL_DS), but s390 opts out.
> >
> > - Why doesn't x86 set HAVE_FUTEX_CMPXCHG? Or do we still support
> > some 32-bit configurations that don't have cmpxchg and don't know
> > about it at compile time?
>
> I'm not entirely sure. Have to dig into the details. I assume S390 just can
> set it though.

x86 as well. It's supported from 486 onwards and we ripped out 386 years ago.

Thanks,

tglx