From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751715AbWBELl2 (ORCPT ); Sun, 5 Feb 2006 06:41:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751714AbWBELl2 (ORCPT ); Sun, 5 Feb 2006 06:41:28 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:39844 "EHLO ogre.sisk.pl") by vger.kernel.org with ESMTP id S1750764AbWBELl1 (ORCPT ); Sun, 5 Feb 2006 06:41:27 -0500 From: "Rafael J. Wysocki" To: Pavel Machek Subject: Re: [PATCH -mm] swsusp: freeze user space processes first Date: Sun, 5 Feb 2006 12:39:52 +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> <200602051211.07103.rjw@sisk.pl> <20060205111815.GG1790@elf.ucw.cz> In-Reply-To: <20060205111815.GG1790@elf.ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200602051239.53175.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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?] The test code: #include #include int main(int argc, char *argv[]) { vfork(); sleep(300); return 0; } The result: rafael@albercik:~/programming/c> ./vfork_test & [1] 12288 rafael@albercik:~/programming/c> ps l F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND 0 500 6937 6931 17 0 10048 2368 read_c Ss+ pts/1 0:00 /bin/bash 0 500 12139 12133 15 0 10052 2380 wait Ss pts/2 0:00 /bin/bash 0 500 12288 12139 15 0 2420 304 fork D pts/2 0:00 ./vfork_tes 1 500 12291 12288 18 0 2420 304 hrtime S pts/2 0:00 ./vfork_tes 0 500 12372 12139 15 0 3596 820 - R+ pts/2 0:00 ps l rafael@albercik:~/programming/c> kill 12288 rafael@albercik:~/programming/c> ps l F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND 0 500 6937 6931 17 0 10048 2368 read_c Ss+ pts/1 0:00 /bin/bash 0 500 12139 12133 15 0 10052 2380 wait Ss pts/2 0:00 /bin/bash 0 500 12288 12139 15 0 2420 304 fork D pts/2 0:00 ./vfork_tes 1 500 12291 12288 18 0 2420 304 hrtime S pts/2 0:00 ./vfork_tes 0 500 12380 12139 17 0 3600 820 - R+ pts/2 0:00 ps l rafael@albercik:~/programming/c> kill -9 12288 rafael@albercik:~/programming/c> ps l F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND 0 500 6937 6931 17 0 10048 2368 read_c Ss+ pts/1 0:00 /bin/bash 0 500 12139 12133 15 0 10052 2380 wait Ss pts/2 0:00 /bin/bash 0 500 12288 12139 15 0 2420 304 fork D pts/2 0:00 ./vfork_tes 1 500 12291 12288 18 0 2420 304 hrtime S pts/2 0:00 ./vfork_tes 0 500 12387 12139 16 0 3596 816 - R+ pts/2 0:00 ps l rafael@albercik:~/programming/c> Greetings, Rafael