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Re: Using __kuser_cmpxchg
On Thu, 15 Nov 2007, David Daney wrote:
> Paul Brook wrote:
> > > > > 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.
> >
>
> This seems similar to MIPS ll/sc. Perhaps if the arm port were modeled after
> that.
It is when available. But the ARM ll/sc instructions are available only
from architecture level 6, hence not available on many others.
Nicolas