kern/55114: Install fails with "cpu_switchto: switching above IPL_SCHED (8)"

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         55114
>Category:       kern
>Synopsis:       Install fails with "cpu_switchto: switching above IPL_SCHED (8)"
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Mar 27 07:40:00 +0000 2020
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current
>Organization:

>Environment:
System: NetBSD
Architecture: i386
Machine: i386
>Description:

On the TNF i386 testbed, the last few i386 install attempts have all failed
with console messages like these:

  cpu_switchto: switching above IPL_SCHED (8)
  [  69.0954865] cpu0: Begin traceback...
  [  69.0954865] ?(c0100671,c7ef5f10,c7ef5f68,c010066e,c0100671,8,c191e5c0,c1477d80,c1b9e7c0,c093d9f3) at c096a432
  address 0xce47446c is invalid
  address 0xcdf8cc7c is invalid
  address 0xcdf8cc7c is invalid
  address 0xcdf8cc7c is invalid
  address 0xcdf8cc7c is invalid
  address 0xcdf8cc7c is invalid
  address 0xcdf8cc7c is invalid
  address 0xcdf8cc7c is invalid

Full log:

  http://releng.netbsd.org/b5reports/i386/2020/2020.03.27.02.01.48/install.log

The problem started with these commits:

  2020.03.26.19.42.39 ad src/sys/kern/kern_idle.c,v 1.33
  2020.03.26.19.42.39 ad src/sys/kern/kern_synch.c,v 1.345
  2020.03.26.19.46.42 ad src/sys/kern/kern_condvar.c,v 1.44
  2020.03.26.19.46.42 ad src/sys/kern/kern_sleepq.c,v 1.63
  2020.03.26.19.46.42 ad src/sys/kern/kern_turnstile.c,v 1.37
  2020.03.26.19.46.42 ad src/sys/kern/sys_select.c,v 1.53
  2020.03.26.19.46.42 ad src/sys/sys/condvar.h,v 1.15
  2020.03.26.19.46.42 ad src/sys/sys/lwp.h,v 1.203
  2020.03.26.19.46.42 ad src/sys/sys/sleepq.h,v 1.28
  2020.03.26.19.47.23 ad src/sys/sys/param.h,v 1.655
  2020.03.26.20.19.06 ad src/sys/kern/kern_lwp.c,v 1.230
  2020.03.26.20.19.06 ad src/sys/kern/kern_softint.c,v 1.63
  2020.03.26.20.19.06 ad src/sys/sys/intr.h,v 1.20
  2020.03.26.20.19.06 ad src/sys/sys/userret.h,v 1.33
  2020.03.26.21.15.14 ad src/sys/sys/syncobj.h,v 1.13
  2020.03.26.21.25.26 ad src/sys/kern/kern_sig.c,v 1.385
  2020.03.26.21.31.55 ad src/sys/kern/kern_exit.c,v 1.286
  2020.03.26.21.31.55 ad src/sys/kern/kern_lwp.c,v 1.231
  2020.03.26.22.40.10 ad src/sys/rump/librump/rumpkern/sleepq.c,v 1.18
  2020.03.26.22.43.19 ad src/sys/kern/kern_turnstile.c,v 1.38

>How-To-Repeat:

>Fix: