in selectmodule.c, I found the code of epoll module
'        result = epoll_ctl(epfd, op, fd, &ev);
        if (errno == EBADF) {
            /* fd already closed */
            result = 0;
            errno = 0;
        }
'
'man epoll_ctl' show 'EBADF  epfd or fd is not a valid file
descriptor.', assume I register an fd of 'open('xxx', O_RDONLY)', return
value will be -1, errno will be EBADF,  
epoll not support 'file descriptors.' as i know,  or i register an fd
was not be opened.

I don't understand the bug being reported.  The code you quote should 
probably be written as "if (result < 0 && errno == EBADF)", but the block's net effect is to ignore an error by resetting result and errno.  
It doesn't matter if we occasionally set result and errno to 0 when result is already zero, but errno happens to be set to EBADF from some earlier operation.

The open('xxx', O_RDONLY) would raise an exception, not return a fd of -1, so I don't see how that can be used to trigger a problem.

Therefore I'll close this issue, but am willing to re-open it if someone can explain a way this code could actually cause problems.