panic: mtx_lock() of spin mutex (null) @ /syzkaller/managers/i386/kernel/sys/netinet/tcp_output.c:337
cpuid = 1
time = 1559774966
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x47/frame 0xfffffe0020eb8520
vpanic() at vpanic+0x1e0/frame 0xfffffe0020eb8580
panic() at panic+0x43/frame 0xfffffe0020eb85e0
__mtx_lock_flags() at __mtx_lock_flags+0x1fd/frame 0xfffffe0020eb8640
tcp_output() at tcp_output+0x5ee/frame 0xfffffe0020eb8800
tcp6_usr_connect() at tcp6_usr_connect+0x3b6/frame 0xfffffe0020eb8870
soconnectat() at soconnectat+0x183/frame 0xfffffe0020eb88d0
kern_connectat() at kern_connectat+0x1ff/frame 0xfffffe0020eb8930
sys_connect() at sys_connect+0xd9/frame 0xfffffe0020eb8970
ia32_syscall() at ia32_syscall+0x452/frame 0xfffffe0020eb8ab0
int0x80_syscall_common() at int0x80_syscall_common+0x9c/frame 0x814247f
KDB: enter: panic
[ thread pid 798 tid 100127 ]
Stopped at      kdb_enter+0x6a: movq    $0,kdb_why