how to continue from a breakpoint in GNU/Hurd

Hi.

I am writing a debugger demo under GNU/Hurd when I study the gdb source
code. And I have met a big problem that when I set a breakpoint in the
inferior, my code can't resume inferior from it.

I can get the exception message from the mach kernel when the inferior hit
the breakpoint. As soon as I got the exception message, I removed the int3,
and set the EIP to the previous values, then post a signal zero to the
inferior by msg_sig_post_untraced_request(). at last I called
thread_resume() to resume it. But thing goes wrong, the inferior is always
stops at the breakpoint. and seems never to continue.

I don't know how to fix this, could any of you give me a suggestion? thanks
very much.

--
Yue Lu (陆岳)