kern/56414: cmake hang on kqueue (condvar waiter list issue) ?

[Manuel.Bouyer%lip6.fr@localhost]

>Number:         56414
>Category:       kern
>Synopsis:       cmake hang on kqueue
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Sep 21 15:00:00 +0000 2021
>Originator:     Manuel Bouyer
>Release:        NetBSD 9.99.77
>Organization:
>Environment:
System: NetBSD amd64-nb9.netbsd.org 9.99.77 NetBSD 9.99.77 (amd64-nb9-PVH) #3: Sun Jan 10 08:56:13 UTC 2021  spz%franklin.NetBSD.org@localhost:/home/netbsd/current/amd64/obj/sys/arch/amd64/compile/amd64-nb9-PVH amd64
Architecture: x86_64
Machine: amd64
>Description:
	In a full pbulk build, I see cmake process hanging on kqueue,
	stalling the build. usually, a kill -STOP/kill -CONT on the
	cmake process wakes it up, and the package build completes without
	issue. This will occur several times in a pbulk run.
	This has been discussed several times on NetBSD's lists,
	as in
	http://mail-index.netbsd.org/tech-kern/2021/01/12/msg027056.html
	https://mail-index.netbsd.org/current-users/2021/04/06/msg040695.html

>How-To-Repeat:
	run and monitor a full pbulk build on a -current host
>Fix: