From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750699AbXBRLdN (ORCPT ); Sun, 18 Feb 2007 06:33:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750710AbXBRLdM (ORCPT ); Sun, 18 Feb 2007 06:33:12 -0500 Received: from mail.screens.ru ([213.234.233.54]:49853 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750704AbXBRLdJ (ORCPT ); Sun, 18 Feb 2007 06:33:09 -0500 Date: Sun, 18 Feb 2007 14:32:59 +0300 From: Oleg Nesterov To: "Rafael J. Wysocki" Cc: ego@in.ibm.com, akpm@osdl.org, paulmck@us.ibm.com, mingo@elte.hu, vatsa@in.ibm.com, dipankar@in.ibm.com, venkatesh.pallipadi@intel.com, linux-kernel@vger.kernel.org, Pavel Machek Subject: Re: [RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug Message-ID: <20070218113259.GB100@tv-sign.ru> References: <20070214144031.GA15257@in.ibm.com> <200702172324.44892.rjw@sisk.pl> <20070217234201.GA591@tv-sign.ru> <200702181132.41264.rjw@sisk.pl> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200702181132.41264.rjw@sisk.pl> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On 02/18, Rafael J. Wysocki wrote: > > On Sunday, 18 February 2007 00:42, Oleg Nesterov wrote: > > On 02/17, Rafael J. Wysocki wrote: > > > > > > On Saturday, 17 February 2007 22:34, Oleg Nesterov wrote: > > > > > > > > static inline int is_user_space(struct task_struct *p) > > > > { > > > > return p->mm && !(p->flags & PF_BORROWED_MM); > > > > } > > > > > > > > This doesn't look right. First, an exiting task has ->mm == NULL after > > > > do_exit()->exit_mm(). Probably not a problem. However, PF_BORROWED_MM > > > > check is racy without task_lock(), so we can have a false positive as > > > > well. Is it ok? We can freeze aio_wq prematurely. > > > > > > Right now aio_wq is not freezeable (PF_NOFREEZE). > > > > Right now yes, but we are going to change this? > > Well, is there any more reliable (and not racy) method of differentiating > between kernel threads and user space processes? Not that I know of. At least, we can take task_lock() to really rule out kernel threads at FREEZER_USER_SPACE stage. Oleg.