Using __kuser_cmpxchg

[Paul Brook]

> >  > In the mean time you can work around it by using a mutex around the
> >  > thread state modification instead of using cmpxchg on it.  Or if your
> >  > platform is ARMv6 or higher then you won't get those spurious false
> >  > negatives.
> >
> > Ah, OK, that's interesting: it sounds like you understand under what
> > circumstances it may fail "spuriously".
>
> Heh, I wrote that code (and comment).  :-)
>
> > What are these?
>
> On a pre-ARMv6 processor

Similar "spurious" failures can happen on ARMv6 processors.

ARMv6 cpus don't have atomic operations either. They have ldrex/strex, where 
the latter will fail if another CPU modifies the memory *or* a context switch 
occurs.

Paul