kern/56764: panic assertion "uvmexp.swpgonly > 0"

[prlw1%cam.ac.uk@localhost]

>Number:         56764
>Category:       kern
>Synopsis:       panic assertion "uvmexp.swpgonly > 0"
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Mar 21 09:35:00 +0000 2022
>Originator:     Patrick Welche
>Release:        NetBSD-9.99.95/amd64 20 Mar 2022
>Organization:
>Environment:
>Description:
During "shutdown -p now" of a pbulk run that was swapping heavily (has
something changed with libreoffice?), the following panic happened
(leaving disks needing fsck -y)

(gdb) print panicstr
$1 = 0xffffffff8151cc80 <scratchstr> "kernel diagnostic assertion \"uvmexp.swpgonly > 0\" failed: file \"../../../../uvm/uvm_swap.c\", line 1830 "
(gdb) bt
#0  0xffffffff802229c5 in cpu_reboot (howto=howto@entry=260, 
    bootstr=bootstr@entry=0x0) at ../../../../arch/amd64/amd64/machdep.c:720
#1  0xffffffff80aca704 in kern_reboot (howto=howto@entry=260, 
    bootstr=bootstr@entry=0x0) at ../../../../kern/kern_reboot.c:73
#2  0xffffffff80b0db72 in vpanic (
    fmt=0xffffffff80fce6f0 "kernel %sassertion \"%s\" failed: file \"%s\", line %d ", ap=ap@entry=0xffffab04b0be4ad8) at ../../../../kern/subr_prf.c:290
#3  0xffffffff80c81c8f in kern_assert (
    fmt=fmt@entry=0xffffffff80fce6f0 "kernel %sassertion \"%s\" failed: file \"%s\", line %d ") at ../../../../../../lib/libkern/kern_assert.c:51
#4  0xffffffff80a8793d in uvm_swap_get (page=<optimized out>, 
    page@entry=0xffffab0020000d00, swslot=<optimized out>, flags=flags@entry=2)
    at ../../../../uvm/uvm_swap.c:1830
#5  0xffffffff80a6798e in uvmfault_anonget (ufi=ufi@entry=0x0, 
    amap=amap@entry=0xffff9665d0e40198, anon=anon@entry=0xffff9665db0cdad8)
    at ../../../../uvm/uvm_fault.c:392
#6  0xffffffff80a61bb8 in uvm_anon_pagein (amap=amap@entry=0xffff9665d0e40198, 
    anon=0xffff9665db0cdad8) at ../../../../uvm/uvm_anon.c:287
#7  0xffffffff80a60ad2 in amap_swap_off (startslot=1, endslot=122095319)
    at ../../../../uvm/uvm_amap.c:1402
#8  0xffffffff80a8513b in swap_off (l=l@entry=0xffff9665e3dde480, 
    sdp=0xffff9665d12ed100) at ../../../../uvm/uvm_swap.c:1082
#9  0xffffffff80a86af7 in sys_swapctl (l=0xffff9665e3dde480, 
    uap=0xffffab04b0be4f00, retval=<optimized out>)
    at ../../../../uvm/uvm_swap.c:748
#10 0xffffffff803fd09e in sy_call (rval=0xffffab04b0be4eb0, 
    uap=0xffffab04b0be4f00, l=0xffff9665e3dde480, 
    sy=0xffffffff814639e8 <sysent+6504>) at ../../../../sys/syscallvar.h:65
#11 sy_invoke (code=271, rval=0xffffab04b0be4eb0, uap=0xffffab04b0be4f00, 
    l=0xffff9665e3dde480, sy=0xffffffff814639e8 <sysent+6504>)
    at ../../../../sys/syscallvar.h:94
#12 syscall (frame=0xffffab04b0be4f00)
    at ../../../../arch/x86/x86/syscall.c:138
#13 0xffffffff8020867d in handle_syscall ()
#14 0x0000000000000002 in ?? ()
#15 0x00007f7fffffd7f0 in ?? ()
#16 0x0000000000000000 in ?? ()
(gdb) print uvmexp
$5 = {pagesize = 4096, pagemask = 4095, pageshift = 12, npages = 16245534, 
  free = 5948528, paging = 0, wired = 4978, ncolors = 16, colormask = 15, 
  zeropages = 0, reserve_pagedaemon = 1, reserve_kernel = 80, 
  anonpages = 12304, filepages = 6062858, execpages = 16584, freemin = 4096, 
  freetarg = 5461, wiredmax = 5415178, nswapdev = 1, swpages = 122095317, 
  swpgavail = 0, swpginuse = 2, swpgonly = 0, nswget = 1903783, 
  faults = 1647202138, traps = 1648322817, intrs = 4570866, swtch = 73563035, 
  softs = 8174162, syscalls = -1962293868, pageins = 68644, _unused1 = 0, 
  _unused2 = 0, pgswapin = 0, pgswapout = 5382281, forks = 2573596, 
  forks_ppwait = 1630951, forks_sharevm = 1630951, pga_zerohit = 0, 
  pga_zeromiss = 0, zeroaborts = 0, colorhit = 1333019305, 
  colormiss = 139555180, cpuhit = 1156296487, cpumiss = 316277998, 
  fltnoram = 11842172, fltnoanon = 0, fltpgwait = 53, fltpgrele = 0, 
  fltrelck = 452245, fltrelckok = 452073, fltanget = 59468194, 
  fltanretry = 68735, fltamcopy = 157083835, fltnamap = 55460761, 
  fltnomap = 1168414334, fltlget = 326455861, fltget = 415713, 
  flt_anon = 35398387, flt_acow = 24037224, flt_obj = 245215384, 
  flt_prcopy = 81224287, flt_przero = 1245736078, pdwoke = 3499331, 
  pdrevs = 1612, _unused3 = 0, pdfreed = 31670364, pdscans = 62863648, 
  pdanscan = 229129, pdobscan = 31441586, pdreact = 35679, pdbusy = 0, 
  pdpageouts = 337035, pdpending = 5045166, pddeact = 66951433, pdreanon = 0, 
  pdrefile = 0, pdreexec = 0, bootpages = 507705}

>How-To-Repeat:

>Fix: