From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965280AbXDBJU6 (ORCPT ); Mon, 2 Apr 2007 05:20:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965267AbXDBJU6 (ORCPT ); Mon, 2 Apr 2007 05:20:58 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:45208 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965280AbXDBJU5 (ORCPT ); Mon, 2 Apr 2007 05:20:57 -0400 Date: Mon, 2 Apr 2007 14:58:18 +0530 From: Srivatsa Vaddagiri To: Ingo Molnar Cc: Gautham R Shenoy , akpm@linux-foundation.org, paulmck@us.ibm.com, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, Oleg Nesterov , "Rafael J. Wysocki" , dipankar@in.ibm.com, dino@in.ibm.com, masami.hiramatsu.pt@hitachi.com Subject: Re: [RFC] Cpu-hotplug: Using the Process Freezer (try2) Message-ID: <20070402092818.GE2456@in.ibm.com> Reply-To: vatsa@in.ibm.com References: <20070402053457.GA9076@in.ibm.com> <20070402061612.GA7072@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070402061612.GA7072@elte.hu> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 02, 2007 at 08:16:12AM +0200, Ingo Molnar wrote: > hm, shouldnt the make be frozen immediately? > > doesnt the 'please freeze ASAP' flag get propagated to all tasks, > immediately? After that point any cloning activity should duplicate that > flag too, resulting in any new child freezing immediately too. afaics, setting the 'please freeze asap' flag is racy wrt dup_task_struct (where the child's tsk->thread_info->flags are copied from its parent?). Secondly, from what I understand, it takes a 'flag to be set + signal marked pending' for the child task to be frozen. If that is the case, then copy_process may not propogae the signal to the child, which could mean mean that we can be in a catch-up game in freeze_processes, trying to freeze processes we didnt see in earlier passes. I think copy_process() can check for something like this: write_lock_irq(&tasklist_lock); ... if (freezing(current)) freeze_process(p); /* function exported by freezer */ ... write_unlock_irq(&tasklist_lock); -- Regards, vatsa