zfs panic when 'make buildworld buildkernel'

[YAMAMOTO Shigeru]

Hi,

I try to 'make buildworld buildkernel' at full ZFS environment.
But I can't finished buildworld/buildkernel without panic.
Anyone have same trouble?

uname -a:
```
FreeBSD jenkins-02.current.os-hackers.jp 13.0-CURRENT FreeBSD 13.0-CURRENT
#0 r366657: Tue Oct 13 13:07:15 JST 2020
root at jenkins-02.current.os-hackers.jp:/usr/obj/usr/src/amd64.amd64/sys/GENERIC
amd64
```

panic message:
```
login: panic: VERIFY(tid) failed

cpuid = 2
time = 1602582381
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame
0xfffffe002abaa9f0
vpanic() at vpanic+0x182/frame 0xfffffe002abaaa40
spl_panic() at spl_panic+0x3a/frame 0xfffffe002abaaaa0
taskq_dispatch() at taskq_dispatch+0xe8/frame 0xfffffe002abaaae0
arc_prune_async() at arc_prune_async+0x3f/frame 0xfffffe002abaab00
arc_evict_cb() at arc_evict_cb+0x1f6/frame 0xfffffe002abaab60
zthr_procedure() at zthr_procedure+0x8f/frame 0xfffffe002abaabb0
fork_exit() at fork_exit+0x80/frame 0xfffffe002abaabf0
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe002abaabf0
--- trap 0, rip = 0, rsp = 0, rbp = 0 ---
KDB: enter: panic
[ thread pid 19 tid 100070 ]
Stopped at      kdb_enter+0x37: movq    $0,0x10b0116(%rip)
db>
```

Latest stable kernel, I have, is:
```
FreeBSD jenkins-02.current.os-hackers.jp 13.0-CURRENT FreeBSD 13.0-CURRENT
#0 r363746: Sat Aug  1 14:25:06 JST 2020
root at freebsd-00.current.os-hackers.jp:/usr/obj/usr/src/amd64.amd64/sys/GENERIC
amd64
```

Thanks,
---
YAMAMOTO Shigeru <shigeru at os-hackers.jp>