From: Oleg Nesterov <oleg@tv-sign.ru>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Davide Libenzi <davidel@xmailserver.org>,
Ingo Molnar <mingo@elte.hu>,
Linus Torvalds <torvalds@linux-foundation.org>,
Roland McGrath <roland@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] will_become_orphaned_pgrp: we have threads
Date: Sun, 9 Dec 2007 17:21:16 +0300 [thread overview]
Message-ID: <20071209142116.GB131@tv-sign.ru> (raw)
In-Reply-To: <m11w9wpx03.fsf@ebiederm.dsl.xmission.com>
On 12/08, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@tv-sign.ru> writes:
>
> > p->exit_state != 0 doesn't mean this process is dead, it may have sub-threads.
> >
> > However, the new "p->exit_state && thread_group_empty(p)" check is not correct
> > either, this is just the temporary hack. Perhaps we can just remove this check,
> > but I don't understand orphaned process groups magic. At all. However, I think
> > exit_notify() is obviously and completely wrong wrt this helper.
>
> The problem that orphaned processes groups address is what happens if
> an entire process group is stopped, and there is not a process that
> can wake them up.
>
> The rule for an unprivileged process sending a signal to a process
> group is that it must be in the same session as the process group.
>
> The rule for sending a signal to a process group is that the signal sender
> must be in the same session.
>
> So we are testing for a process group that does not have a living
> member with a parent outside of the process that can send the process
> group a signal.
Ah, thanks a lot Eric, I am _starting_ to understand this.
> Oleg what do you see wrong with checking p->exit_state &&
> thread_group_empty(p)? Since non-leader threads all self reap
> that seems to be a valid test for an dead thread group.
There is a window when exit_notify() drops tasklist and before release_task().
Suppose the last (non-leader) thread exits. This means that entire group exits,
but thread_group_empty() is not true.
Oleg.
next prev parent reply other threads:[~2007-12-09 14:20 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-08 18:38 [PATCH 1/3] will_become_orphaned_pgrp: we have threads Oleg Nesterov
2007-12-08 23:50 ` Eric W. Biederman
2007-12-09 14:21 ` Oleg Nesterov [this message]
2007-12-09 15:45 ` Eric W. Biederman
2007-12-09 16:43 ` Oleg Nesterov
2007-12-09 23:56 ` Eric W. Biederman
2007-12-10 18:37 ` Oleg Nesterov
2007-12-11 1:36 ` Eric W. Biederman
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