panic: mtx_lock() of spin mutex (null) @ /syzkaller/managers/main/kernel/sys/netinet/tcp_output.c:337
cpuid = 1
time = 1559700019
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x47/frame 0xfffffe0020ef9550
vpanic() at vpanic+0x1e0/frame 0xfffffe0020ef95b0
panic() at panic+0x43/frame 0xfffffe0020ef9610
__mtx_lock_flags() at __mtx_lock_flags+0x1fd/frame 0xfffffe0020ef9670
tcp_output() at tcp_output+0x5ee/frame 0xfffffe0020ef9830
tcp_usr_connect() at tcp_usr_connect+0x25c/frame 0xfffffe0020ef9880
soconnectat() at soconnectat+0x183/frame 0xfffffe0020ef98e0
kern_connectat() at kern_connectat+0x1ff/frame 0xfffffe0020ef9940
sys_connect() at sys_connect+0xd9/frame 0xfffffe0020ef9980
amd64_syscall() at amd64_syscall+0x436/frame 0xfffffe0020ef9ab0
fast_syscall_common() at fast_syscall_common+0x101/frame 0xfffffe0020ef9ab0
--- syscall (198, FreeBSD ELF64, nosys), rip = 0x4131ba, rsp = 0x7fffdfffdf38, rbp = 0x3 ---
KDB: enter: panic
[ thread pid 848 tid 100141 ]
Stopped at      kdb_enter+0x6a: movq    $0,kdb_why