netmgr/netmgr.c:1737: (...) failed

Hi!

I am seeing this for some internal DNS queries:

$ host www.unesp.br 200.145.86.1
Using domain server:
Name: 200.145.86.1
Address: 200.145.86.1#53
Aliases: 

www.unesp.br has address 200.145.6.98
netmgr/netmgr.c:1737: REQUIRE((((handle) != ((void *)0) && ((const isc__magic_t *)(handle))->magic == ((('N') << 24 | ('M') << 16 | ('H') << 8 | ('D')))) && __extension__ ({ __auto_type __atomic_load_ptr = (&(handle)->references); __typeof__ ((void)0, *__atomic_load_ptr) __atomic_load_tmp; __atomic_load (__atomic_load_ptr, &__atomic_load_tmp, (5)); __atomic_load_tmp; }) > 0)) failed, back trace
/usr/lib/x86_64-linux-gnu/libisc-9.17.20-2-Debian.so(+0x3552f)[0x7fae10e0f52f]
/usr/lib/x86_64-linux-gnu/libisc-9.17.20-2-Debian.so(isc_assertion_failed+0xa)[0x7fae10e0f48a]
/usr/lib/x86_64-linux-gnu/libisc-9.17.20-2-Debian.so(isc__nmhandle_attach+0x63)[0x7fae10df9aa3]
host(+0xe3aa)[0x55c5f12963aa]
host(+0xf2c7)[0x55c5f12972c7]
host(+0x1177b)[0x55c5f129977b]
/usr/lib/x86_64-linux-gnu/libisc-9.17.20-2-Debian.so(isc__nm_async_readcb+0xad)[0x7fae10dfce6d]
/usr/lib/x86_64-linux-gnu/libisc-9.17.20-2-Debian.so(isc__nm_readcb+0x97)[0x7fae10dfcf97]
/usr/lib/x86_64-linux-gnu/libisc-9.17.20-2-Debian.so(+0x30cd0)[0x7fae10e0acd0]
/usr/lib/x86_64-linux-gnu/libisc-9.17.20-2-Debian.so(isc__nm_udp_read_cb+0x46)[0x7fae10e0c4c6]
/usr/lib/x86_64-linux-gnu/libuv.so.1(+0x1ee8d)[0x7fae10956e8d]
/usr/lib/x86_64-linux-gnu/libuv.so.1(+0x22c75)[0x7fae1095ac75]
/usr/lib/x86_64-linux-gnu/libuv.so.1(uv_run+0x114)[0x7fae10947854]
/usr/lib/x86_64-linux-gnu/libisc-9.17.20-2-Debian.so(+0x247da)[0x7fae10dfe7da]
/usr/lib/x86_64-linux-gnu/libisc-9.17.20-2-Debian.so(isc__trampoline_run+0x16)[0x7fae10e36bd6]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x8eae)[0x7fae10b36eae]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x3f)[0x7fae10a66a5f]
zsh: IOT instruction (core dumped)  host www.unesp.br 200.145.86.1

I hope that some of these files are helpful :-)

core dump

gdb's "thread apply all bt full"

tcpdump output

This is also https://bugs.debian.org/1000447

If you need anything else, just let me know, please.

Thank you!