Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755334AbXLJKED (ORCPT ); Mon, 10 Dec 2007 05:04:03 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751764AbXLJKDw (ORCPT ); Mon, 10 Dec 2007 05:03:52 -0500 Received: from E23SMTP03.au.ibm.com ([202.81.18.172]:49387 "EHLO e23smtp03.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751577AbXLJKDw (ORCPT ); Mon, 10 Dec 2007 05:03:52 -0500 Date: Mon, 10 Dec 2007 13:49:52 +0530 From: Gautham R Shenoy To: Ingo Molnar Cc: Jiri Slaby , Andrew Morton , linux-kernel@vger.kernel.org, "Rafael J. Wysocki" , Arjan van de Ven , Thomas Gleixner , Linux-pm mailing list , Dipankar Sarma Subject: Re: broken suspend (sched related) [Was: 2.6.24-rc4-mm1] Message-ID: <20071210081952.GA7215@in.ibm.com> Reply-To: ego@in.ibm.com References: <20071204211701.994dfce6.akpm@linux-foundation.org> <47595A0A.5000502@gmail.com> <20071207151150.GB24254@elte.hu> <20071207175134.GA18916@elte.hu> <475A5188.6070809@gmail.com> <20071208083939.GD30997@elte.hu> <475A629C.7010408@gmail.com> <20071208152447.GA30270@elte.hu> <475B24F4.3090904@gmail.com> <20071209074647.GE22981@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071209074647.GE22981@elte.hu> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3452 Lines: 127 On Sun, Dec 09, 2007 at 08:46:47AM +0100, Ingo Molnar wrote: > > * Jiri Slaby wrote: > > > On 12/08/2007 04:24 PM, Ingo Molnar wrote: > > > i'm wondering why it had no effect now > > > > diff --git a/kernel/cpu.c b/kernel/cpu.c > > index e0d3a4f..a46c252 100644 > > --- a/kernel/cpu.c > > +++ b/kernel/cpu.c > > @@ -47,15 +47,21 @@ void __init cpu_hotplug_init(void) > > } > > > > #ifdef CONFIG_HOTPLUG_CPU > > - > > +#include > > void get_online_cpus(void) > > { > > + outb(0x20, 0x80); > > might_sleep(); > > + outb(0x21, 0x80); > > ah. If you comment out get_online_cpus()/put_online_cpus() from > kernel/softlockup.c, does it start working? > > Gautham, any ideas? Hi Ingo, >From the code I fail to see how get_online_cpus() can help us. + /* + * Only do the hung-tasks check on one CPU: + */ + get_online_cpus(); + check_cpu = any_online_cpu(cpu_online_map); + put_online_cpus(); check_cpu can go offline here, no? + + if (this_cpu != check_cpu) + continue; + + if (sysctl_hung_task_timeout_secs) + check_hung_uninterruptible_tasks(this_cpu); Further more this can cause a deadlock since we're calling get_online_cpus() from the watchdog thread's context, which is going to be kthread_stop'ed from a cpu-hotplug context. This is what I think was happening in the case reported by Jiri. Please find the patch below. Thanks and Regards gautham. commit 15bfb662b35c609490185fba2fd4713d230b9374 Author: Gautham R Shenoy Date: Mon Dec 10 13:41:45 2007 +0530 softlockup: remove get_online_cpus() which doesn't help here. The get_online_cpus() protection seems to be bogus in kernel/softlockup.c as cpu cached in check_cpu can go offline once we do a put_online_cpus(). This can also cause deadlock during a cpu offline as follows: WATCHDOG_THREAD: OFFLINE_CPU: mutex_down(&cpu_hotplug.lock); /* All subsequent get_online_cpus * will be blocked till we're * done with this cpu-hotplug * operation. */ get_online_cpus(); /* watchdog is blocked Thus we cannot go further until the cpu-hotplug operation completes */ CPU_DEAD: kthread_stop(watchdog_thread); /* we're trying to stop a * thread which is blocked * waiting for us to finish. * * Since we cannot finish until * the thread stops, we deadlock here! */ Signed-off-by: Gautham R Shenoy Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Arjan van de Van Cc: Jiri Slaby diff --git a/kernel/softlockup.c b/kernel/softlockup.c index e50b44a..576eb9c 100644 --- a/kernel/softlockup.c +++ b/kernel/softlockup.c @@ -219,9 +219,7 @@ static int watchdog(void *__bind_cpu) /* * Only do the hung-tasks check on one CPU: */ - get_online_cpus(); check_cpu = any_online_cpu(cpu_online_map); - put_online_cpus(); if (this_cpu != check_cpu) continue; -- Gautham R Shenoy Linux Technology Center IBM India. "Freedom comes with a price tag of responsibility, which is still a bargain, because Freedom is priceless!" -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/