Kernel Panic on boot after clean reboot

[namezero111111]

Dear folks,

we have an embedded device running 19.1 i386 nano version.
An admin rebooted the device via WebGUI and it never came back online.

Connecting via serial console, the output shows a failure to load netgraph.ko due to an undefined symbol.

Now we fixed this through reflashing and restoring, but this is very disconcerting to just write off as strange occurence.

We have excluded:
- CF card; it checks out OK
- Unclean shutdown; it was rebooted via webgui and fstab mounted with noatime,sync


We'd appreciate any input as to what might cause this so as to prevent this in the future..

Here's the output:

/boot/kernel/kernel text=0x1409269 data=0xee088+0x28e534 syms=[0x4+0xf6f50+0x4+0x18b906]
/boot/entropy size=0x1000
/boot/kernel/if_gre.ko text=0x3118 data=0x278+0x30 syms=[0x4+0xa30+0x4+0xab9]
/boot/kernel/if_tap.ko text=0x3734 data=0x2dc+0x34 syms=[0x4+0xa70+0x4+0x9f6]
/boot/kernel/pf.ko text=0x35ca8 data=0x4e8+0x1128 syms=[0x4+0x2490+0x4+0x2a0c]
/boot/kernel/carp.ko text=0x8150 data=0x374+0x74 syms=[0x4+0xe90+0x4+0xf1c]
/boot/kernel/if_bridge.ko text=0x7c40 data=0x350+0x3c syms=[0x4+0xff0+0x4+0x11f2]
loading required module 'bridgestp'
/boot/kernel/bridgestp.ko text=0x4994 data=0xe0+0x18 syms=[0x4+0x6d0+0x4+0x66b]
/boot/kernel/if_lagg.ko text=0xa024 data=0x294+0x28 syms=[0x4+0xf20+0x4+0x108a]
/boot/kernel/ng_UI.ko text=0x908 data=0x128 syms=[0x4+0x3a0+0x4+0x352]
loading required module 'netgraph'
/boot/kernel/netgraph.ko text=0xb348 data=0x474+0x8c syms=[0x4+0x14c0+0x4+0x1984]
/boot/kernel/ng_async.ko text=0x1b10 data=0x158 syms=[0x4+0x5b0+0x4+0x5e4]
/boot/kernel/ng_bpf.ko text=0x2370 data=0x158 syms=[0x4+0x5f0+0x4+0x66d]
/boot/kernel/ng_bridge.ko text=0x2604 data=0x158+0x20 syms=[0x4+0x6b0+0x4+0x780]
/boot/kernel/ng_cisco.ko text=0x1814 data=0x128 syms=[0x4+0x540+0x4+0x508]
/boot/kernel/ng_echo.ko text=0x4ec data=0x128 syms=[0x4+0x2f0+0x4+0x2f7]
/boot/kernel/ng_eiface.ko text=0x19f0 data=0x148+0x4 syms=[0x4+0x6e0+0x4+0x707]
/boot/kernel/ng_ether.ko text=0x2398 data=0x14c+0x4 syms=[0x4+0x760+0x4+0x7c9]
/boot/kernel/ng_frame_relay.ko text=0xe90 data=0x128 syms=[0x4+0x3e0+0x4+0x3be]
/boot/kernel/ng_hole.ko text=0x934 data=0x128 syms=[0x4+0x3c0+0x4+0x3b4]
/boot/kernel/ng_iface.ko text=0x1e04 data=0x178+0x4 syms=[0x4+0x6f0+0x4+0x746]
/boot/kernel/ng_ksocket.ko text=0x3208 data=0x158 syms=[0x4+0x850+0x4+0x94f]
/boot/kernel/ng_l2tp.ko text=0x3e64 data=0x158 syms=[0x4+0x720+0x4+0x7ce]
/boot/kernel/ng_l2tp.ko text=0x3e64 data=0x158 syms=[0x4+0x720+0x4+0x7ce]
can't load file '/boot/kernel/ng_l2tp.ko': input/output error
/boot/kernel/ng_lmi.ko text=0x24e0 data=0x128 syms=[0x4+0x4b0+0x4+0x43a]
/boot/kernel/ng_mppc.ko text=0x3ab0 data=0x25c+0x4 syms=[0x4+0x760+0x4+0x89d]
loading required module 'rc4'
/boot/kernel/rc4.ko text=0x3d0 data=0xe0 syms=[0x4+0x250+0x4+0x224]
/boot/kernel/ng_one2many.ko text=0x1420 data=0x128 syms=[0x4+0x500+0x4+0x592]
/boot/kernel/ng_ppp.ko text=0x601c data=0x158 syms=[0x4+0x8c0+0x4+0x974]
/boot/kernel/ng_pppoe.ko text=0x534c data=0x15c syms=[0x4+0x740+0x4+0x790]
/boot/kernel/ng_pptpgre.ko text=0x3068 data=0x128 syms=[0x4+0x5c0+0x4+0x5f8]
/boot/kernel/ng_rfc1490.ko text=0x12e8 data=0x128 syms=[0x4+0x440+0x4+0x41e]
/boot/kernel/ng_socket.ko text=0x2830 data=0x4a8+0x18 syms=[0x4+0x9e0+0x4+0xb4b]
/boot/kernel/ng_tee.ko text=0xe7c data=0x128 syms=[0x4+0x440+0x4+0x42b]
/boot/kernel/ng_tty.ko text=0x1724 data=0x148 syms=[0x4+0x570+0x4+0x4d4]
/boot/kernel/ng_vjc.ko text=0x2430 data=0x128 syms=[0x4+0x5c0+0x4+0x5d6]
/boot/kernel/ng_vlan.ko text=0x16d0 data=0x128 syms=[0x4+0x4f0+0x4+0x50e]
/boot/kernel/if_enc.ko text=0x1118 data=0x2b8+0x8 syms=[0x4+0x690+0x4+0x813]
/boot/kernel/pflog.ko text=0x10f0 data=0x11c+0x44 syms=[0x4+0x540+0x4+0x55b]
/boot/kernel/pfsync.ko text=0x7e5c data=0x228+0x160 syms=[0x4+0xd40+0x4+0xd84]
/boot/kernel/ng_car.ko text=0x1c94 data=0x1a0 syms=[0x4+0x540+0x4+0x543]
/boot/kernel/ng_deflate.ko text=0x1b34 data=0x174 syms=[0x4+0x600+0x4+0x6c0]
/boot/kernel/ng_pipe.ko text=0x2b0c data=0x158+0x1c syms=[0x4+0x6b0+0x4+0x6c1]
/boot/kernel/ng_pred1.ko text=0x1ac4 data=0x158 syms=[0x4+0x530+0x4+0x594]
/boot/kernel/ng_tcpmss.ko text=0xe74 data=0x128 syms=[0x4+0x420+0x4+0x465]
Booting...
KDB: debugger backends: ddb
KDB: current backend: ddb
Copyright (c) 1992-2017 The FreeBSD Project.
Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
        The Regents of the University of California. All rights reserved.
FreeBSD is a registered trademark of The FreeBSD Foundation.
FreeBSD 11.1-RELEASE-p6  6621d681e(stable/18.1) i386
FreeBSD clang version 4.0.0 (tags/RELEASE_400/final 297347) (based on LLVM 4.0.0)
VT(vga): resolution 640x480
[HBSD HARDENING] procfs hardening: enabled
[HBSD ASLR] status: opt-out
[HBSD ASLR] mmap: 14 bit
[HBSD ASLR] exec base: 14 bit
[HBSD ASLR] stack: 14 bit
[HBSD ASLR] vdso: 8 bit
[HBSD LOG] logging to system: enabled
[HBSD LOG] logging to user: disabled
[HBSD SEGVGUARD] status: opt-out
[HBSD SEGVGUARD] expiry: 120 sec
[HBSD SEGVGUARD] suspension: 600 sec
[HBSD SEGVGUARD] maxcrashes: 5
link_elf: symbol ▒▒▒▒▒▒▒▒▒▒▒▒U▒▒SWV▒▒]▒▒x▒E▒M▒PQS▒u
▒
 undefined
KLD file netgraph.ko - could not finalize loading
KLD file ng_UI.ko - cannot find dependency "netgraph"
KLD file ng_async.ko - cannot find dependency "netgraph"
KLD file ng_bpf.ko - cannot find dependency "netgraph"
KLD file ng_bridge.ko - cannot find dependency "netgraph"
KLD file ng_cisco.ko - cannot find dependency "netgraph"
KLD file ng_echo.ko - cannot find dependency "netgraph"
KLD file ng_eiface.ko - cannot find dependency "netgraph"
KLD file ng_ether.ko - cannot find dependency "netgraph"
KLD file ng_frame_relay.ko - cannot find dependency "netgraph"
KLD file ng_hole.ko - cannot find dependency "netgraph"
KLD file ng_iface.ko - cannot find dependency "netgraph"
KLD file ng_ksocket.ko - cannot find dependency "netgraph"
KLD file ng_lmi.ko - cannot find dependency "netgraph"
KLD file ng_mppc.ko - cannot find dependency "netgraph"
KLD file ng_one2many.ko - cannot find dependency "netgraph"
KLD file ng_ppp.ko - cannot find dependency "netgraph"
KLD file ng_pppoe.ko - cannot find dependency "netgraph"
KLD file ng_pptpgre.ko - cannot find dependency "netgraph"
KLD file ng_rfc1490.ko - cannot find dependency "netgraph"
KLD file ng_socket.ko - cannot find dependency "netgraph"
KLD file ng_tee.ko - cannot find dependency "netgraph"
KLD file ng_tty.ko - cannot find dependency "netgraph"
KLD file ng_vjc.ko - cannot find dependency "netgraph"
KLD file ng_vlan.ko - cannot find dependency "netgraph"
KLD file ng_car.ko - cannot find dependency "netgraph"
KLD file ng_deflate.ko - cannot find dependency "netgraph"
KLD file ng_pipe.ko - cannot find dependency "netgraph"
KLD file ng_pred1.ko - cannot find dependency "netgraph"
KLD file ng_tcpmss.ko - cannot find dependency "netgraph"
CPU: Geode(TM) Integrated Processor by AMD PCS (498.06-MHz 586-class CPU)
  Origin="AuthenticAMD"  Id=0x5a2  Family=0x5  Model=0xa  Stepping=2
  Features=0x88a93d<FPU,DE,PSE,TSC,MSR,CX8,SEP,PGE,CMOV,CLFLUSH,MMX>
  AMD Features=0xc0400000<MMX+,3DNow!+,3DNow!>
real memory  = 268435456 (256 MB)
avail memory = 230801408 (220 MB)
pnpbios: Bad PnP BIOS data checksum
random: unblocking device.
Timecounter "TSC" frequency 498061502 Hz quality 800
taskqgroup_adjust failed cnt: 1 stride: 1 mp_ncpus: 1 smp_started: 0
taskqgroup_adjust failed cnt: 1 stride: 1 mp_ncpus: 1 smp_started: 0
random: entropy device external interface
wlan: mac acl policy registered
kbd0 at kbdmux0
panic: vm_fault: fault on nofault entry, addr: d18a8000
cpuid = 0
KDB: stack backtrace:
db_trace_self_wrapper(c2022a7c,56be1d6c,c1ad48f8,c1630899,c2022a44,...) at db_trace_self_wrapper+0x2a/frame 0xc20229a0
kdb_backtrace(0,0,0,d18a8000,d18a8000,...) at kdb_backtrace+0x2e/frame 0xc2022a00
vpanic(c1630899,c2022a44,c2022a44,c2022af8,c0f90355,...) at vpanic+0x10e/frame 0xc2022a24
panic(c1630899,d18a8000,c189c370,7af4800,1,...) at panic+0x14/frame 0xc2022a38
vm_fault_hold(c23e1000,d18a8000,1,0,0) at vm_fault_hold+0x1f55/frame 0xc2022af8
vm_fault(c23e1000,d18a8000,1,0) at vm_fault+0x69/frame 0xc2022b20
trap_pfault(d18a883c) at trap_pfault+0xcc/frame 0xc2022b64
trap(c2022c68) at trap+0x2b3/frame 0xc2022c5c
calltrap() at calltrap+0x6/frame 0xc2022c5c
--- trap 0xc, eip = 0xc0cff500, esp = 0xc2022ca8, ebp = 0xc2022cb4 ---
kobj_class_compile(c18360ac) at kobj_class_compile+0xc0/frame 0xc2022cb4
devclass_add_driver(c3de0b80,c18360ac,7fffffff,c1911b7c,c0cc9179,c1911b28,c1911b10) at devclass_add_driver+0x30/frame 0xc2022ccc
driver_module_handler(c3dab1c0,0,c1836094) at driver_module_handler+0x62/frame 0xc2022cfc
module_register_init(c1836088) at module_register_init+0xa0/frame 0xc2022d1c
mi_startup() at mi_startup+0x78/frame 0xc2022d38
begin() at begin+0x22
KDB: enter: panic
[ thread pid 0 tid 100000 ]
Stopped at      kdb_enter+0x35: movl    $0,kdb_why
db>