From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755887Ab1LESnY (ORCPT ); Mon, 5 Dec 2011 13:43:24 -0500 Received: from mail-iy0-f174.google.com ([209.85.210.174]:63676 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755772Ab1LESnX (ORCPT ); Mon, 5 Dec 2011 13:43:23 -0500 Date: Mon, 5 Dec 2011 10:43:15 -0800 From: Tejun Heo To: Frederic Weisbecker Cc: paul@paulmenage.org, rjw@sisk.pl, lizf@cn.fujitsu.com, Linus Torvalds , linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org, matthltc@us.ibm.com, akpm@linux-foundation.org, oleg@redhat.com, kamezawa.hiroyu@Jp.fujitsu.com Subject: Re: [PATCH UPDATED 03/10] threadgroup: extend threadgroup_lock() to cover exit and exec Message-ID: <20111205184315.GJ627@google.com> References: <1320191193-8110-1-git-send-email-tj@kernel.org> <1320191193-8110-4-git-send-email-tj@kernel.org> <20111124225054.GA14828@google.com> <20111125140136.GC23307@somewhere.redhat.com> <20111127193001.GC4266@google.com> <20111202162753.GA19752@somewhere.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111202162753.GA19752@somewhere.redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Frederic. On Fri, Dec 02, 2011 at 05:28:03PM +0100, Frederic Weisbecker wrote: > But I don't think it's very useful to protect against irq_exit_thread(), > what happens there is purely of internal irq interest. > > Then right after, PF_EXITING is set before any interesting change. > Isn't it possible to simply lock this flag setting? IIRC, as soon > as the PF_EXITING flag is set, you ignore the task for attachment. I think that's technically possible but it does introduce another class of tasks - the dying ones. e.g. If a task has PF_EXITING set and the containing process is migrating, we'll have to migrate all tasks but the dying one and cgroup ->exit callbacks can be called on the lonely task after the migration is complete. It's kinda messy and if someone makes a wrong assumption there, the bug is gonna be even more difficult to reproduce / track down than now. Yes, smaller scope locking is nicer but I would like to avoid api weirdities like that. Thanks. -- tejun