From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753879AbXDJOxB (ORCPT ); Tue, 10 Apr 2007 10:53:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753883AbXDJOxB (ORCPT ); Tue, 10 Apr 2007 10:53:01 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:39497 "EHLO ebiederm.dsl.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753879AbXDJOxA (ORCPT ); Tue, 10 Apr 2007 10:53:00 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Ingo Molnar Cc: Oleg Nesterov , Robin Holt , Linus Torvalds , Chris Snook , linux-kernel@vger.kernel.org, Jack Steiner Subject: Re: init's children list is long and slows reaping children. References: <20070405195118.GH22762@lnx-holt.americas.sgi.com> <46159987.6090006@redhat.com> <20070406104301.GB19755@lnx-holt.americas.sgi.com> <20070406163100.GA554@tv-sign.ru> <20070406173249.GA2517@elte.hu> <20070410134814.GA28016@elte.hu> Date: Tue, 10 Apr 2007 08:51:43 -0600 In-Reply-To: <20070410134814.GA28016@elte.hu> (Ingo Molnar's message of "Tue, 10 Apr 2007 15:48:14 +0200") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Ingo Molnar writes: > * Eric W. Biederman wrote: > >> Ingo Molnar writes: >> >> > no. Two _completely separate_ lists. >> > >> > i.e. a to-be-reaped task will still be on the main list _too_. The >> > main list is for all the PID semantics rules. The reap-list is just >> > for wait4() processing. The two would be completely separate. >> >> And what pray tell except for heuristics is the list of children used >> for? > > on a second thought: the p->children list is needed for the whole > child/parent task tree, which is needed for sys_getppid(). Yes, something Oleg said made me realize that. As long as the reparent isn't to complex it isn't required that we have exactly one list . > The question > is, does anything require us to reparent to within the same thread > group? I think my head is finally on straight about this question. Currently there is the silly linux specific parent death signal (pdeath_signal). Oleg's memory was a better than mine on this score. However there is no indication that the parent death signal being sent when a thread leader dies is actually correct, or even interesting. It probably should only be sent when getppid changes. So with pdeath_signal fixed that is nothing that requires us to reparent within the same thread group. I'm trying to remember what the story is now. There is a nasty race somewhere with reparenting, a threaded parent setting SIGCHLD to SIGIGN, and non-default signals that results in an zombie that no one can wait for and reap. It requires being reparented twice to trigger. Anyway it is a real mess and if we can remove the stupid multi-headed child lists things would become much simpler and the problem could not occur. Plus the code would become much simpler... utrace appears to have removed the ptrace_children list and the special cases that entailed. Eric