Re: [PATCH v2] introduce atomic_pointer to fix a race condition in cancelable mcs spinlocks

Paul E. McKenney
2014-06-02T16:47:02Z

On Mon, Jun 02, 2014 at 06:30:32PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 02, 2014 at 06:25:25PM +0200, Peter Zijlstra wrote:
> > I'm almost inclined to just exclude parisc from using opt spinning.
> >
> > That said, this patch still doesn't address the far more interesting
> > problem of actually finding these issues for these few weird archs.
>
> So why do these archs provide xchg() and cmpxchg() at all? Wouldn't it
> be much simpler if archs that cannot sanely do this, not provide these
> primitives at all?

Such architectures would also need to avoid NO_HZ_FULL_SYSIDLE and
RCU_NOCB_CPU, but those are probably entirely reasonable restrictions.

Thanx, Paul