linux-kernel - Re: [RFC] Proposal for ptrace improvements

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Message-ID: <20110302074447.GE19669@htj.dyndns.org>
Date:	Wed, 2 Mar 2011 08:44:47 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Indan Zupancic <indan@....nu>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Roland McGrath <roland@...hat.com>, jan.kratochvil@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org
Subject: Re: [RFC] Proposal for ptrace improvements

On Wed, Mar 02, 2011 at 06:07:35AM +0100, Indan Zupancic wrote:
> I'm not sure what Denys is talking about: Currently it's impossible to
> pass along SIGSTOP to traced processes. Quoting the ptrace manpage:
> 
>    PTRACE_CONT
>           Restarts  the stopped child process.  If data is nonzero and not
>           SIGSTOP, it is interpreted as a signal to be  delivered  to  the
>           child;  otherwise,  no  signal is delivered.

AFAICS, that's not true.  SIGSTOP isn't treated differently from other
signals in the ptrace signal delivery path.  Maybe it was true in the
past.

> As for distinguishing STOP signals from stopped childs: Just don't set
> the WUNTRACED flag in the tracer for waitpid.

I'm not following.  Can you please elaborate?

> To me it seems clear that job ctl state should be managed independently
> of ptrace stopped state.  I'm not sure how that fits in with your
> proposed changes, but my impression is that you make everything a lot
> simpler by separating traced stopping/continuing from SIGSTOP/SIGCONT
> job control. It's just not the same. A task stopped by a trace event
> shouldn't generate a STOP signal for it's parent, only for real SIGSTOPS.

Again, not following.  In the proposal, job control and ptrace operate
independently, so on that we seem to agree, but I can't understand
where the STOP signal for the parent comes from?  What are you
referring to?

Thanks.

-- 
tejun
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