linux-kernel - Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after PTRACE

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Date:	Fri, 25 Feb 2011 16:51:42 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Roland McGrath <roland@...hat.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	jan.kratochvil@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after
 PTRACE_ATTACH

Hello,

On Thu, Feb 24, 2011 at 09:29:41PM +0100, Oleg Nesterov wrote:
> Damn. Today is 02/24 ;) sorry.

No need.  I've been pretty lazy with this thread too.  :-)

> > On Fri, Feb 18, 2011 at 08:37:09PM +0100, Oleg Nesterov wrote:
> >
> > > > As it currently stands, SIGSTOP/CONT while ptraced doesn't work
> > >
> > > And this is probably where we disagree the most. I think this is bug,
> > > and this should be fixed.
> >
> > I don't think we disagree that it is a bug.  I want to fix it too but
> > we definitely seem to disagree on how.
> 
> Yes, but I also think that the running tracee in the SIGNAL_STOP_STOPPED
> process is bug by itself. IIUC, you think this is fine.

Yeap, I actually think that's the better way.

> > * ptrace, sans the odd SIGSTOP on attach which we should remove, is
> >   per-task.  Sending out SIGCONT on PTRACE_CONT would break that.  I
> >   really don't think that's a good idea.
> 
> Hmm. But why do you think we should always send SIGCONT after attach?

Hmmm... my sentences were confusing.  I was trying to say,

* ptrace, as it currently stands, is largely per-task.  One exception
  is the implicit SIGSTOP which is sent on PTRACE_ATTACH but this
  should be replaced with a more transparent attach request which
  doesn't affect jctl states.

* Sending out SIGCONT on PTRACE_CONT on jctl stopped tracee adds
  another exception to per-task behavior, which I don't think is a
  good idea.

> > * PTRACE_CONT would be behaving completely differently depending on
> >   whether it's resuming from group stop or other traps.
> 
> Afaics, no. It does not matter from where the tracee resumes. See
> the [pseudo patch] I sent. Once again, it doesn't really work, it
> only tries to explain what I mean.

I see.  I'll read the patch again.

Thanks.

-- 
tejun
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