panic: Assertion pgrp->pg_jobc > 0 failed at kern_proc.c:816

I got this panic again today in a VM when quitting a gdb
session after killing a child process via 'kill'.

panic: Assertion pgrp->pg_jobc > 0 failed at /git/bhyve/sys/kern/kern_proc.c:816
cpuid = 1
time = 1609185862
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe00946547f0
vpanic() at vpanic+0x181/frame 0xfffffe0094654840
panic() at panic+0x43/frame 0xfffffe00946548a0
_refcount_update_saturated() at _refcount_update_saturated/frame 0xfffffe00946548e0
killjobc() at killjobc+0x6a6/frame 0xfffffe0094654940
exit1() at exit1+0x6af/frame 0xfffffe00946549b0
sys_sys_exit() at sys_sys_exit+0xd/frame 0xfffffe00946549c0
amd64_syscall() at amd64_syscall+0x12e/frame 0xfffffe0094654af0
fast_syscall_common() at fast_syscall_common+0xf8/frame 0xfffffe0094654af0
--- syscall (1, FreeBSD ELF64, sys_sys_exit), rip = 0x8024c8f0a, rsp = 0x7fffffffe358, rbp = 0x7fffffffe370 ---
KDB: enter: panic
[ thread pid 44034 tid 102484 ]
Stopped at      kdb_enter+0x37: movq    $0,0x10ab066(%rip)

>From what I can tell, the child process that was killed via 'kill' has
not yet exited and is stuck in ptracestop() from fork():

(kgdb) where
#0  sched_switch (td=0xfffffe0094001a00, flags=<optimized out>) at /git/bhyve/sys/kern/sched_ule.c:2147
#1  0xffffffff80bf4015 in mi_switch (flags=266) at /git/bhyve/sys/kern/kern_synch.c:542
#2  0xffffffff80bfeba5 in thread_suspend_switch (td=<optimized out>, p=<optimized out>)
    at /git/bhyve/sys/kern/kern_thread.c:1477
#3  0xffffffff80bef04b in ptracestop (td=0xfffffe0094001a00, sig=17, si=0x0)
    at /git/bhyve/sys/kern/kern_sig.c:2642
#4  0xffffffff80ba1a54 in fork_return (td=0xfffffe0094001a00, frame=0xfffffe0094671b00)
    at /git/bhyve/sys/kern/kern_fork.c:1106
#5  0xffffffff80ba18b0 in fork_exit (callout=0xffffffff80ba1950 <fork_return>, arg=0xfffffe0094001a00, 
    frame=0xfffffe0094671b00) at /git/bhyve/sys/kern/kern_fork.c:1069
#6  <signal handler called>
#7  0x00000008007b71aa in ?? ()

kgdb can't find the panicking process due to the zombproc removal, so I will
have to go work on kgdb to recover from that change. :(

-- 
John Baldwin