panic: Assertion in_epoch(net_epoch_preempt) failed at /syzkaller/managers/i386/kernel/sys/netinet6/in6_ifattach.c:LINE (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7c87e295 Update some comments; no functional changes. Som..
git tree: freebsd
console output: https://syzkaller.appspot.com/x/log.txt?x=12b9ab53600000
dashboard link: https://syzkaller.appspot.com/bug?extid=805c9fd6ad29f14b2c08
userspace arch: i386
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=146a63d7600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+805c9f...@syzkaller.appspotmail.com

panic: Assertion in_epoch(net_epoch_preempt) failed at
/syzkaller/managers/i386/kernel/sys/netinet6/in6_ifattach.c:251
cpuid = 1
time = 1571269588
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x47/frame
0xfffffe001a154710
vpanic() at vpanic+0x1c7/frame 0xfffffe001a154780
panic() at panic+0x43/frame 0xfffffe001a1547e0
in6_get_hw_ifid() at in6_get_hw_ifid+0x33a/frame 0xfffffe001a154820
nd6_dad_timer() at nd6_dad_timer+0x600/frame 0xfffffe001a1548d0
softclock_call_cc() at softclock_call_cc+0x218/frame 0xfffffe001a1549b0
softclock() at softclock+0xa3/frame 0xfffffe001a1549f0
ithread_loop() at ithread_loop+0x2f2/frame 0xfffffe001a154a60
fork_exit() at fork_exit+0xac/frame 0xfffffe001a154ab0
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe001a154ab0
--- trap 0, rip = 0, rsp = 0, rbp = 0 ---
KDB: enter: panic
[ thread pid 12 tid 100017 ]
Stopped at kdb_enter+0x67: movq $0,0x14776c6(%rip)


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches