From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750796AbWBENgJ (ORCPT ); Sun, 5 Feb 2006 08:36:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750804AbWBENgJ (ORCPT ); Sun, 5 Feb 2006 08:36:09 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:10661 "EHLO ogre.sisk.pl") by vger.kernel.org with ESMTP id S1750796AbWBENgI (ORCPT ); Sun, 5 Feb 2006 08:36:08 -0500 From: "Rafael J. Wysocki" To: Pavel Machek Subject: Re: [PATCH -mm] swsusp: freeze user space processes first Date: Sun, 5 Feb 2006 14:34:40 +0100 User-Agent: KMail/1.9.1 Cc: Ingo Molnar , Andrew Morton , linux-kernel@vger.kernel.org, nigel@suspend2.net References: <200602051014.43938.rjw@sisk.pl> <20060205111815.GG1790@elf.ucw.cz> <200602051239.53175.rjw@sisk.pl> In-Reply-To: <200602051239.53175.rjw@sisk.pl> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200602051434.41686.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sunday 05 February 2006 12:39, Rafael J. Wysocki wrote: > On Sunday 05 February 2006 12:18, Pavel Machek wrote: > > On Ne 05-02-06 12:11:06, Rafael J. Wysocki wrote: > > > On Sunday 05 February 2006 11:50, Ingo Molnar wrote: > > > > > > > > * Rafael J. Wysocki wrote: > > > > > > > > > > The logic in that loop makes my brain burst. > > > > > > > > > > > > What happens if a process does vfork();sleep(100000000)? > > > > > > > > > > The freezing of processes will fail due to the timeout. > > > > > > > > > > Without the if (!p->vfork_done) it would fail too, because the child > > > > > would be frozen and the parent would wait for the vfork completion in > > > > > the TASK_UNINTERRUPTIBLE state (ie. unfreezeable). But in that case > > > > > we have a race between the "freezer" and the child process (ie. if the > > > > > child gets frozen before it completes the vfork completion, the paret > > > > > will be unfreezeable) which sometimes leads to a failure when it > > > > > should not. [We have a test case showing this.] > > > > > > > > then i'd suggest to change the vfork implementation to make this code > > > > freezable. > > > > > > I think you are right, but I don't know how to do this. > > > > > > > Nothing that userspace does should cause freezing to fail. If it does, > > > > we've designed things incorrectly on the kernel side. > > > > > > I tend to agree. > > > > > > Generally, the problem is due to the use of completions where userland > > > processes are waited for. The two places I know of are the vfork > > > implementation and the usermode helper code. > > > > Can you produce userland testcase? If we have uninterruptible process for > > days... that's a bug in kernel, suspend or not. > > Sure, no problem. [Pretty scary, no?] Actually it's not that bad, because the parent will be killable when the child exit()s (or gets killed). Greetings, Rafael