kern/55850: resize_ffs test regression on amd64

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

>Number:         55850
>Category:       kern
>Synopsis:       resize_ffs test regression on amd64
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Dec 08 09:20:00 +0000 2020
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current
>Organization:
>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

The following test cases now fail on amd64, but not on i386:

  sbin/resize_ffs/t_grow:grow_16M_v0_8192
  sbin/resize_ffs/t_grow:grow_16M_v1_16384
  sbin/resize_ffs/t_grow:grow_16M_v2_32768
  sbin/resize_ffs/t_grow_swapped:grow_16M_v0_65536
  sbin/resize_ffs/t_grow_swapped:grow_16M_v1_4096
  sbin/resize_ffs/t_grow_swapped:grow_16M_v2_8192
  sbin/resize_ffs/t_shrink:shrink_24M_16M_v0_32768
  sbin/resize_ffs/t_shrink:shrink_24M_16M_v1_65536
  sbin/resize_ffs/t_shrink_swapped:shrink_24M_16M_v0_4096
  sbin/resize_ffs/t_shrink_swapped:shrink_24M_16M_v1_8192

The fail both under qemu/nvmm and on real hardware.  The problem
started some time during the period of build breakage that began
with the commit

  2020.12.05.18.17.01 thorpej src/sys/kern/init_main.c 1.534
  2020.12.05.18.17.01 thorpej src/sys/kern/kern_clock.c 1.143
  2020.12.05.18.17.01 thorpej src/sys/kern/kern_exec.c 1.504
  2020.12.05.18.17.01 thorpej src/sys/kern/kern_exit.c 1.291
  2020.12.05.18.17.01 thorpej src/sys/kern/kern_time.c 1.207
  2020.12.05.18.17.01 thorpej src/sys/sys/param.h 1.681
  2020.12.05.18.17.01 thorpej src/sys/sys/proc.h 1.368
  2020.12.05.18.17.01 thorpej src/sys/sys/timevar.h 1.45

and ended with:

  2020.12.06.15.00.25 christos src/external/gpl3/gdb/bin/Makefile 1.4

Logs:

  http://releng.netbsd.org/b5reports/amd64/commits-2020.12.html#2020.12.06.15.00.25

>How-To-Repeat:

Run the ATF tests on amd64.

>Fix: