Upcoming feature freeze vs. concurrency change

[Torvald Riegel]

I have been working on a new, more scalable rwlock implementation.  The
last information I have about the feature freeze is stating July 1st.
Is this still up to date?  I believe I'll need a few more days to finish
the rwlock if all works well, but I won't make Jul 1st because I'm AFK
tomorrow till Sunday.  Would this still be acceptable?

Second, it would be good to add spinning to various concurrent code,
starting with pthread mutexes were it would likely provide most benefit.
This would be purely a performance optimization.  Would this still be
acceptable to do early during the freeze period?

Third, I've posted the new condition variable a while ago.  This hasn't
been fully reviewed so far, but I believe it would be eligible for 2.24
because it's been posted before the freeze deadline.

Thoughts?