panic: assertion "sym->vs_refs > 0" failed in varsymdrop at /usr/src/sys/kern/kern_varsym.c:492
Trace beginning at frame 0xfffff80117f83838
varsymdrop() at varsymdrop+0x4e 0xffffffff8062269e 
varsymdrop() at varsymdrop+0x4e 0xffffffff8062269e 
varsymset_clean() at varsymset_clean+0x57 0xffffffff80622ed7 
exit1() at exit1+0x59 0xffffffff8063f779 
sys_exit() at sys_exit+0xe 0xffffffff8063fdfe 
syscall2() at syscall2+0x11e 0xffffffff80bd6a0e 
Stopped at      Debugger+0x7c:  movb    $0,0xbdaf09(%rip)
db>