login: panic: mtx_lock() of spin mutex (null) @ /syzkaller/managers/main/kernel/sys/netinet/tcp_output.c:337 cpuid = 1 time = 1552890865 KDB: stack backtrace: db_trace_self_wrapper() at db_trace_self_wrapper+0x47/frame 0xfffffe0021263530 vpanic() at vpanic+0x1e0/frame 0xfffffe0021263590 panic() at panic+0x43/frame 0xfffffe00212635f0 __mtx_lock_flags() at __mtx_lock_flags+0x1fd/frame 0xfffffe0021263650 tcp_output() at tcp_output+0x62a/frame 0xfffffe0021263810 tcp6_usr_connect() at tcp6_usr_connect+0x3b6/frame 0xfffffe0021263880 soconnectat() at soconnectat+0x183/frame 0xfffffe00212638e0 kern_connectat() at kern_connectat+0x1ff/frame 0xfffffe0021263940 sys_connect() at sys_connect+0xd9/frame 0xfffffe0021263980 amd64_syscall() at amd64_syscall+0x436/frame 0xfffffe0021263ab0 fast_syscall_common() at fast_syscall_common+0x101/frame 0xfffffe0021263ab0 --- syscall (198, FreeBSD ELF64, nosys), rip = 0x412e5a, rsp = 0x7fffdfffdf38, rbp = 0x3 --- KDB: enter: panic [ thread pid 793 tid 100126 ] Stopped at kdb_enter+0x6a: movq $0,kdb_why