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Date: Thu, 5 Sep 2002 18:29:47 -0400
From: Daniel Jacobowitz <dan@debian.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
       Linus Torvalds <torvalds@transmeta.com>, linux-kernel@vger.kernel.org
Subject: Re: [patch] ptrace-fix-2.5.33-A1
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On Fri, Sep 06, 2002 at 12:25:32AM +0200, Ingo Molnar wrote:
> 
> On Thu, 5 Sep 2002, Daniel Jacobowitz wrote:
> 
> > Right - let me rephrase.  Tasks which are either:
> >   - untraced, normal
> >   - traced, but traced _by their parent_
> > are on the sibling/children list.
> 
> hm, why the distinction along whether the debugger == real parent? What
> wrong can happen if we always move traced tasks to the ptrace list? The
> task will be both in the ptrace list and in the parent's child list, and 
> everything should work as expected. This looks a more symmetric and 
> simpler thing to me.

Hmm, I like that idea.  But I was talking about current implementation. 
If we want to do this then we'd need to fix up every ptrace
implementation in every architecture to call the appropriate function;
it's a separate problem.

> > > this splitup of the lists makes it possible for the debugger to do a wait4
> > > that will get events from the debugged task, and for the debugged task to
> > > also be available to the real parent.
> > 
> > Great.  I'm not exactly sure on how this works right now: sys_wait4 only
> > iterates over ->children, with the exception of the special code in
> > TASK_ZOMBIE.  I'm not quite sure when events from a traced process get
> > to the normal parent of that process, or when they're supposed to.
> 
> i'm not sure about this either. What happens if an (untraced) parent has
> traced and untraced children, and does a wait4. Would it confuse the
> debugger if the parent could get one of the traced tasks as a result in
> wait4? And how does the debugger solve this problem?

Well, it seems to me that when a traced task has an event, it should be
reported first to the debugger - for signals this happens in do_signal
- and then possibly to the normal parent.  But I'm not sure if this
actually happens right now or not.  Worth investigating some more.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer
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