panic: sx_xlock() of destroyed sx @ /syzkaller/managers/main/kernel/sys/kern/uipc_sockbuf.c:282
cpuid = 0
time = 1552788887
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x47/frame 0xfffffe001fa5e4f0
vpanic() at vpanic+0x1e0/frame 0xfffffe001fa5e550
panic() at panic+0x43/frame 0xfffffe001fa5e5b0
_sx_xlock() at _sx_xlock+0x1c9/frame 0xfffffe001fa5e600
sblock() at sblock+0xeb/frame 0xfffffe001fa5e630
vn_sendfile() at vn_sendfile+0x650/frame 0xfffffe001fa5e8e0
sendfile() at sendfile+0x155/frame 0xfffffe001fa5e980
amd64_syscall() at amd64_syscall+0x436/frame 0xfffffe001fa5eab0
fast_syscall_common() at fast_syscall_common+0x101/frame 0xfffffe001fa5eab0
--- syscall (198, FreeBSD ELF64, nosys), rip = 0x412e5a, rsp = 0x7fffdffdcf38, rbp = 0x4 ---
KDB: enter: panic
[ thread pid 796 tid 100122 ]
Stopped at      kdb_enter+0x6a: movq    $0,kdb_why