Message-ID: <43DF36EF.C38E6C4B@tv-sign.ru>
Date: Tue, 31 Jan 2006 13:07:43 +0300
From: Oleg Nesterov <oleg@tv-sign.ru>
MIME-Version: 1.0
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] exec: Cleanup exec from a non thread group leader.
References: <43DDFDE3.58C01234@tv-sign.ru> <43DE2730.795468DC@tv-sign.ru> <m1vew15ud4.fsf@ebiederm.dsl.xmission.com>
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"Eric W. Biederman" wrote:
> 
> Oleg Nesterov <oleg@tv-sign.ru> writes:
> 
> > Oleg Nesterov wrote:
> >>
> >> Eric W. Biederman wrote:
> >> >
> >> > -     list_add_tail(&thread->tasks, &init_task.tasks);
> >>
> >> The last deletion is wrong, I beleive.
> >
> > Just to clarify, it looks like we can kill this line because
> > de_thread() also does list_add_tail(current, &init_task.tasks).
> >
> > But please note that it (and probably __ptrace_link() above)
> > does list_del(current->task) first, and current->task may have
> > very stale values after old leader called dup_task_struct().
> > SET_LINKS() in copy_process() does nothing with ->tasks in a
> > CLONE_THREAD case.
> 
> Good point in that instance we need to remove the list_del
> as well.

We can't just remove this list_del, note __ptrace_link() above.
So if we remove list_add from switch_exec_pids() (like you did
in your patch) we should also place list_add before ptrace_link()
in de_thread(), otherwise I beleive it is a bug.

I agree, we should cleanup this. I just noticed that I forgot
to add you on CC: list while sending this patch:

	http://marc.theaimsgroup.com/?l=linux-kernel&m=113862839924746

Btw, I don't understand why __ptrace_link() use REMOVE_LINKS/SET_LINKS
instead of remove_parent/add_parent.

Oleg.
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