On Wed, Dec 28, 2016 at 8:08 PM, Nicholas Piggin <npiggin@gmail.com> wrote:
>
> Okay. The name could be a bit better though I think, for readability.
> Just a BUILD_BUG_ON if it is not constant and correct bit numbers?

I have a slightly edited patch - moved the comments around and added
some new comments (about both the sign bit, but also about how the
smp_mb() shouldn't be necessary even for the non-atomic fallback).

I also did a BUILD_BUG_ON(), except the other way around - keeping it
about the sign bit in the byte, just just verifying that yes,
PG_waiters is that sign bit.

> BTW. I just notice in your patch too that you didn't use "nr" in the
> generic version.

And I fixed that too.

Of course, I didn't test the changes (apart from building it). But
I've been running the previous version since yesterday, so far no
issues.

                Linus