linux-kernel - Re: Testing lxc 0.6.5 in Fedora 13

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Message-ID: <20100406143635.GA12315@redhat.com>
Date:	Tue, 6 Apr 2010 16:36:35 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Matt Helsley <matthltc@...ibm.com>
Cc:	Roland McGrath <roland@...hat.com>,
	Grzegorz Nosek <root@...aldomain.pl>,
	Sukadev Bhattiprolu <sukadev@...ibm.com>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org,
	Biederman Eric Biederman <ebiederm@...ssion.com>
Subject: Re: Testing lxc 0.6.5 in Fedora 13

On 04/06, Matt Helsley wrote:
>
> On Mon, Apr 05, 2010 at 08:44:43PM -0700, Roland McGrath wrote:
>
> > tracehook_report_clone_complete() call is made when that task_struct is no
> > longer guaranteed to be valid.

Hmm. I missed this.

> Also, if utrace allows multiple tracers and they each
> exist in a different namespace then storing a pid nr isn't going to work.

Yes, but utrace is simple. ptrace_report_clone() does

	ctx->eventmsg = child->pid;

we should fix this line and that is all, afaics. Every tracer has a
separate "struct ptrace_context *ctx".

> So my hunch is, in the long run, we'll need to hold a reference there and
> drop it when the last tracer detaches

Without utrace only one tracer is possible.

So, I think we should either change do_fork() to get the right tracee_pid_nr,
or add get/put into do_fork() and change tracehooks as Roland suggested.

Oleg.

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