From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754392AbZHaTbT (ORCPT ); Mon, 31 Aug 2009 15:31:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754003AbZHaTbT (ORCPT ); Mon, 31 Aug 2009 15:31:19 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:53670 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752635AbZHaTbS (ORCPT ); Mon, 31 Aug 2009 15:31:18 -0400 From: "Rafael J. Wysocki" To: Jiri Slaby Subject: Re: suspend race -next regression [Was: Power: fix suspend vt regression] Date: Mon, 31 Aug 2009 21:32:10 +0200 User-Agent: KMail/1.12.0 (Linux/2.6.31-rc8-rjw; KDE/4.3.0; x86_64; ; ) Cc: Greg KH , linux-kernel@vger.kernel.org, Alan Cox , Ingo Molnar References: <1249980093-16319-1-git-send-email-jirislaby@gmail.com> <4A81E073.5080703@gmail.com> <4A9B9C1C.9020506@gmail.com> In-Reply-To: <4A9B9C1C.9020506@gmail.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <200908312132.10904.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Monday 31 August 2009, Jiri Slaby wrote: > On 08/11/2009 11:19 PM, Jiri Slaby wrote: > > However there is still a race or something. Sometimes the suspend goes > > through, sometimes it doesn't. I will investigate this further. > > Hmm, this took a loong time to track down a bit. Code instrumentation by > outb(XX, 0x80) usually caused the issue to disappear. > > However I found out that it's caused by might_sleep() calls in > flush_workqueue() and flush_cpu_workqueue(). I.e. it looks like there is > a task which deadlocks/spins forever. If we won't reschedule to it, > suspend proceeds. > > I replaced the latter might_sleep() by show_state() and removed > refrigerated tasks afterwards. The thing is that I don't know if the > prank task is there. I need a scheduler to store "next" task pid or > whatever to see what it picked as "next" and so what will run due to > might_sched(). I can then show it on port 80 display and read it when > the hangup occurs. > > Depending on which might_sleep(), either flush_workqueue() never (well, > at least in next 5 minutes) proceeds to for_each_cpu() or > wait_for_completion() in flush_cpu_workqueue() never returns. > > It's a regression against some -rc1 based -next tree. Bisection > impossible, suspend needs to be run even 7 times before it occurs. Maybe > a s/might_sleep/yield/ could make it happen earlier (going to try)? If /sys/class/rtc/rtc0/wakealarm works on this box, you can use it to trigger resume in a loop. Basically, you can do # echo 0 > /sys/class/rtc/rtc0/wakealarm # date +%s -d "+60 seconds" > /sys/class/rtc/rtc0/wakealarm then go to suspend and it will resume the box in ~1 minute. Thanks, Rafael