[uml-devel] Re: Stop at startup on 2.6 NPTL hosts

["Sven Köhler" <skoehler@upb.de>]

> It is one UML bug I've just identified and that I'm trying to fix. This is the 
> faulty code, from arch/um/kernel/skas/process.c:
> 
> static int userspace_tramp(void *arg)
> {
>         init_new_thread_signals(0);
>         enable_timer();
>         ptrace(PTRACE_TRACEME, 0, 0, 0);
>         tkill(gettid(), SIGSTOP);
>         os_stop_process(os_getpid());
>         return(0);
> }
> 
> This is executed by a clone() child. What happens is that, with NPTL, both the 
> father and the son have the same pid, so the SIGSTOP is routed to the wrong 
> thread. However, this is not expected: having the same pid should be reserved 
> to when clone is called with CLONE_THREAD in the flags. I've verified that 
> this is not happening in this case, even with strace (to make sure glibc is 
> not playing any dirty tricks). But for some reasons, the kernel is behaving 
> as if this happened.

This does remind me of something. I've already read the whole thing with 
CLONE_THREAD and clone() somewhere else, but i can't remember where it 
was. Was it on UML-MailingLists? Or was it even on the LKML? If my brain 
would just be a bit more reliable :-(


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