On Fri, 2009-05-01 at 17:46 -0400, Kyle McMartin wrote:
> On Fri, May 01, 2009 at 05:37:18PM -0400, John David Anglin wrote:
> > On Fri, 01 May 2009, Carlos O'Donell wrote:
> >
> > > Historical note...
> > >
> > > We clobber all of memory in userspace, like this:
> > > ~~~
> > > #define __ldcw(a) \
> > > ({ \
> > > unsigned int __ret; \
> > > __asm__ __volatile__("ldcw 0(%1),%0" \
> > > : "=r" (__ret) : "r" (a) : "memory"); \
> > > __ret; \
> > > })
> > > ~~~
> > > I wonder if I should change that to match the kernel?
> >
> > The above is perfectly safe. I believe the kernel provides a memory
> > barrier when necessary. There's a discussion somewhere in the mail
> > archives.
> >
>
> I, er, don't think we do, not for the spinlock primitives at least, as
> far as I can tell...
Yes we do ... look in asm/spinlock.h
it's all the mb(); statements that are scattered through our _raw_spin_
ops
The original problem was that the spinlocks were compile barrier leaky
and caused infrequent but hard to debug issues on smp. The barriers are
likely overkill (since we have two in each) but at least they prevent
problems.
James
--
To unsubscribe from this list: send the line "unsubscribe linux-parisc" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
