linux-kernel - Re: [PATCHSET ptrace] ptrace: implement PTRACE_SEIZE/INTERRUPT and group stop notification, take#4

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Date:	Fri, 3 Jun 2011 17:46:32 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Tejun Heo <tj@...nel.org>, jan.kratochvil@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu, bdonlan@...il.com,
	pedro@...esourcery.com
Subject: Re: [PATCHSET ptrace] ptrace: implement PTRACE_SEIZE/INTERRUPT and
	group stop notification, take#4

On 06/03, Denys Vlasenko wrote:
>
> On Friday 03 June 2011 03:24, Tejun Heo wrote:
> >
> > Anyways, let's think about that, but SIGSTOP on clone is closely
> > linked to why SEIZE is used in the first place and I currently lean
> > toward tying it to SEIZE.
>
> Ok.
>
> SIGSTOP on clone is less problematic because in practice it's
> rather hard to send a real SIGSTOP to a thread which is _just_ created.
> So the race window is mostly theoretical

It is not. The new child can dequeue a signal which was sent to the
process (thread group). How the tracer can distinguish? Also, SIGSTOP
can be sent to pgrp and the new tracee can be forked.

I think that SEIZE should never send SIGSTOP on auto-attach, without
any options.

Oleg.

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