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

From: "Sven Köhler" <skoehler@upb.de>
To: Blaisorblade <blaisorblade_spam@yahoo.it>
Cc: user-mode-linux-devel@lists.sourceforge.net,
	Jeff Dike <jdike@addtoit.com>, Roland Kaeser <roli8200@yahoo.de>,
	Nuno Silva <nuno.silva@vgertech.com>,
	Antoine Martin <antoine@nagafix.co.uk>,
	Dennis Muhlestein <devel@muhlesteins.com>
Subject: [uml-devel] Re: Stop at startup on 2.6 NPTL hosts
Date: Wed, 03 Nov 2004 00:43:36 +0100	[thread overview]
Message-ID: <41881BA8.80102@upb.de> (raw)
In-Reply-To: <200411021952.09095.blaisorblade_spam@yahoo.it>

> 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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