kernel bug in 11.3-STABLE causes frequent crashes

[Scott Bennett]

     I have had to waste a great deal of time lately in recovering my
system from crashes due to a kernel bug.  At present, my system is

FreeBSD hellas 11.3-STABLE FreeBSD 11.3-STABLE #12 r352571: Sat Sep 21 11:39:52 CDT 2019     bennett at hellas:/usr/obj/usr/src/sys/hellas  amd64

There are actually at least two problems, but this particular one has been
causing a large portion of my forced reboots.  It usually fails to produce
a dump and freezes right after the panic and backtrace messages, as it did
earlier tonight, but Wednesday night it did create a dump, which I am
keeping in case it should prove helpful in getting the bug identified and
solved.  I copied the console messages to paper painstakingly by hand.
They appear to be identical each time, except, of course, for the messages
that a dump is produced when, indeed, it does produce one.  I am omitting
those fairly standard messages.

Fatal trap 12: page fault while in kernel mode
cpuid = 2; apic id = 02
fault virtual address   = 0x3b8
fault code              = supervisor read data, page not present
instruction pointer     = 0x20:0xffffffff80a4b14c
stack pointer           = 0x0:0xfffffe012a60ea50
frame pointer           = 0x0:0xfffffe012a60eae0
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 28 (flowcleaner)
trap number             = 12
panic: page fault
cpuid = 2
KDB: stack backtrace:
#0 0xffffffff80a94707 at kdb_backtrace+0x67
#1 0xffffffff80a4fa2e at vpanic+0x17e
#2 0xffffffff80a4f8a3 at panic+0x43
#3 0xffffffff80f3a4d0 at trap_pfault+0
#4 0xffffffff80f3a519 at trap_pfault+0x49
#5 0xffffffff80f39bad at trap+0x29
#6 0xffffffff80f19f33 at calltrap+0x8
#7 0xffffffff80b3bb8d at flowtable_clean_vnet+0x43d
#8 0xffffffff80b3c758 at flowtable_cleaner+0xc8
#9 0xffffffff80a12ea2 at fork_exit+0x82
#10 0xffffffff80flaf4e at fork_trampoline+0xe

     The machine is ancient.  The CPU is a QX9650 (last group of Core 2
Quads) with 8 GB of DDR3 memory.
     If this can be identified as a known bug and a clue provided to a
patch or a safer version to upgrade to, I would be grateful.  I am getting
very, very tired of these crashes.
     The other forced reboots I will describe in a separate message, but
that problem has existed since the time of 11.2-RELEASE and apparently was
never investigated, much less fixed, although people began complaining on
this list and possibly -questions within the first few days after the
release date.
     Thanks in advance for any help with this problem!


                                  Scott Bennett, Comm. ASMELG, CFIAG
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