linux-kernel - Re: [PATCH] ptrace: make former thread ID available via PTRACE_GETEVENTMSG after PTRACE_EVENT

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Message-ID: <20110627134713.GB3527@redhat.com>
Date:	Mon, 27 Jun 2011 15:47:13 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ptrace: make former thread ID available via
	PTRACE_GETEVENTMSG after PTRACE_EVENT_EXEC stop (v.2)

On 06/27, Tejun Heo wrote:
>
> Hello, Oleg, Denys.
>
> On Sun, Jun 26, 2011 at 10:04:42PM +0200, Oleg Nesterov wrote:
> > May be PT_TRACE_EXEC makes more sense. Note that
> > ptrace_event_enabled() was recently added.
>
> Do we want to enable this silently?  Wouldn't it be better to make it
> dependent on PT_SEIZED?

Hmm. Not sure I understand. Why can't PTRACE_SEIZE add PT_TRACE_EXEC
(and PT_TRACESYSGOOD) along with PT_SEIZED during attach?

I think this makes more sense, this way the tracer can disable this
later via PTRACE_SETOPTIONS if it wants. Not that I think this is really
useful but still. Otherwise we are going to silently disable
PTRACE_O_TRACEEXEC, this may be confusing.

But. If we want the PT_TRACE_EXEC behaviour for PT_SEIZED task (personally
I think we do), then we should probably record the old pid unconditionally,
the tracer can attach later.

Even in this case ptrace_event(PTRACE_EVENT_EXEC) can race with detach +
attach in theory, but I think in this case we do not care.

Oleg.

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