named crashed during loading zones on OpenBSD

The xferquota system test started to fail on main (79d5a67e) often (but not always) on OpenBSD 6.8. The CI job usually timeouts https://gitlab.isc.org/isc-projects/bind9/-/jobs/1288958 - it's not clear why.

S:xferquota:2020-11-10T20:35:39+0100
T:xferquota:1:A
A:xferquota:System test xferquota
I:xferquota:PORTS:23476,23477,23478,23479,23480,23481,23482,23483,23484,23485,23486
I:xferquota:starting servers
I:xferquota:Have       50 zones up in 1 seconds
I:xferquota:Changing test zone...
I:xferquota:Have       70 zones up in 2 seconds
I:xferquota:Have       90 zones up in 3 seconds
I:xferquota:Have      110 zones up in 4 seconds
I:xferquota:Have      130 zones up in 5 seconds
I:xferquota:Have      150 zones up in 6 seconds
I:xferquota:Have      170 zones up in 7 seconds
I:xferquota:Have      190 zones up in 8 seconds
I:xferquota:Have      210 zones up in 9 seconds
I:xferquota:Have      212 zones up in 10 seconds
I:xferquota:Have      212 zones up in 11 seconds
I:xferquota:Have      212 zones up in 12 seconds
...
I:xferquota:Have      212 zones up in 355 seconds
I:xferquota:Have      212 zones up in 356 seconds
I:xferquota:Have      212 zones up in 357 seconds
I:xferquota:Have      212 zones up in 358 seconds
I:xferquota:Have      212 zones up in 359 seconds
I:xferquota:Took too long to load zones
I:xferquota:stopping servers
I:xferquota:ns2 died before a SIGTERM was sent
I:xferquota:stopping servers failed
I:xferquota:Core dump(s) found: xferquota/ns2/named.core 
D:xferquota:backtrace from xferquota/ns2/named.core:
D:xferquota:--------------------------------------------------------------------------------
D:xferquota:Core was generated by `named'.
D:xferquota:Program terminated with signal SIGABRT, Aborted.
D:xferquota:#0  thrkill () at /tmp/-:3
D:xferquota:[Current thread is 1 (process 237557)]
D:xferquota:#0  thrkill () at /tmp/-:3
D:xferquota:#1  0x000007a0ce20f4ee in _libc_abort () at /usr/src/lib/libc/stdlib/abort.c:51
D:xferquota:#2  0x0000079ec861f833 in assertion_failed (file=<optimized out>, line=<optimized out>, type=<optimized out>, cond=<optimized out>) at main.c:254
D:xferquota:#3  0x000007a145240ae0 in isc_assertion_failed (file=0x0, line=6, type=isc_assertiontype_require, cond=0x7a0ce1ccc2a <thrkill+10> "r\001\303d\211\004% ") at assertions.c:46
D:xferquota:#4  0x000007a14522034a in isc_nmhandle_detach (handlep=<optimized out>) at netmgr/netmgr.c:1319
D:xferquota:#5  0x000007a14884d474 in xfrin_connect_done (handle=0x0, result=5, cbarg=<optimized out>) at xfrin.c:964
D:xferquota:#6  0x000007a145226999 in tcpdnsconnect_cb (handle=<optimized out>, result=5, arg=<optimized out>) at netmgr/tcpdns.c:791
D:xferquota:#7  0x000007a145225058 in failed_connect_cb (sock=<optimized out>, req=0x0, eresult=5) at netmgr/tcp.c:136
D:xferquota:#8  0x000007a1452225da in tcp_connect_direct (sock=0x7a1b9a41010, req=0x7a1ac303000) at netmgr/tcp.c:208
D:xferquota:#9  0x000007a145222202 in isc__nm_async_tcpconnect (worker=<optimized out>, ev0=<optimized out>) at netmgr/tcp.c:235
D:xferquota:#10 0x000007a1452217b0 in process_queue (worker=0x7a0faea7508, queue=0x7a109166f00) at netmgr/netmgr.c:642
D:xferquota:#11 0x000007a145221bae in process_normal_queue (worker=0x0) at netmgr/netmgr.c:594
D:xferquota:#12 0x000007a145221567 in process_queues (worker=0x7a0faea7508) at netmgr/netmgr.c:602
D:xferquota:#13 0x000007a14521ddee in async_cb (handle=<optimized out>) at netmgr/netmgr.c:560
D:xferquota:#14 0x000007a13517d588 in uv.async_io () from /usr/local/lib/libuv.so.2.1
D:xferquota:#15 0x000007a13518e6d5 in uv.io_poll () from /usr/local/lib/libuv.so.2.1
D:xferquota:#16 0x000007a13517dc31 in uv_run () from /usr/local/lib/libuv.so.2.1
D:xferquota:#17 0x000007a14521de8b in nm_thread (worker0=0x7a0faea7508) at netmgr/netmgr.c:500
D:xferquota:#18 0x000007a1b8889e21 in _rthread_start (v=<optimized out>) at /usr/src/lib/librthread/rthread.c:96
D:xferquota:#19 0x000007a0ce243168 in __tfork_thread () at /usr/src/lib/libc/arch/amd64/sys/tfork_thread.S:77
D:xferquota:#20 0x0000000000000000 in ?? ()
D:xferquota:--------------------------------------------------------------------------------
D:xferquota:full backtrace from xferquota/ns2/named.core saved in named.core-backtrace.txt
D:xferquota:core dump xferquota/ns2/named.core archived as xferquota/ns2/named.core.gz
R:xferquota:FAIL
E:xferquota:2020-11-10T20:41:56+0100
FAIL: xferquota

NS2 named.run:

10-Nov-2020 20:35:53.276 netmgr/netmgr.c:1319: REQUIRE(((__builtin_expect(!!((*handlep) != ((void *)0)), 1) && __builtin_expect(!!(((const isc__magic_t *)(*handlep))->magic == ((('N') << 24 | ('M') << 16 | ('H') << 8 | ('D')))), 1)) && __c11_atomic_load(&(*handlep)->references, 5) > 0)) failed
10-Nov-2020 20:35:53.276 exiting (due to assertion failure)

named.core.gz

named.core-backtrace.txt

named.run

xferquota.log