Re: "Verifying and Optimizing Compact NUMA-Aware Locks on Weak Memory Models"

[Paul E. McKenney]

On Mon, Aug 29, 2022 at 04:33:23AM +0200, Andrea Parri wrote:
> On Fri, Aug 26, 2022 at 05:48:12AM -0700, Paul E. McKenney wrote:
> > Hello!
> > 
> > I have not yet done more than glance at this one, but figured I should
> > send it along sooner rather than later.
> > 
> > "Verifying and Optimizing Compact NUMA-Aware Locks on Weak
> > Memory Models", Antonio Paolillo, Hernán Ponce-de-León, Thomas
> > Haas, Diogo Behrens, Rafael Chehab, Ming Fu, and Roland Meyer.
> > https://arxiv.org/abs/2111.15240
> > 
> > The claim is that the queued spinlocks implementation with CNA violates
> > LKMM but actually works on all architectures having a formal hardware
> > memory model.
> > 
> > Thoughts?
> 
> Section 4 ends with a discussion about certain "spurious" data races.
> Do we have litmus tests with them?  (I could repro with Dartagnan...)

Their Figure 5 clearly shows a data race, but agreed, their claim is
that this race is prevented by other code not in this litmus test.
Me, I currently suspect that the spurious data race might be due to the
failure to guarantee mutual exclusion, though I have not yet read that
paper carefully.  That is scheduled for tomorrow morning.

							Thanx, Paul