code: func (inode *Inode) DeRef(n uint64) (stale bool) {
  	inode.logFuse("DeRef", n, inode.refcnt)
  
  	if inode.refcnt < n {
  		panic(fmt.Sprintf("deref %v from %v", n, inode.refcnt))
  	}
  
  	inode.refcnt -= n
  
  	stale = (inode.refcnt == 0)
  	return
  }
docs: // LOCKS_REQUIRED(fs.mu)