From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754711Ab1KUS0M (ORCPT ); Mon, 21 Nov 2011 13:26:12 -0500 Received: from e23smtp03.au.ibm.com ([202.81.31.145]:53290 "EHLO e23smtp03.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752121Ab1KUS0J (ORCPT ); Mon, 21 Nov 2011 13:26:09 -0500 Message-ID: <4ECA97B7.8010102@linux.vnet.ibm.com> Date: Mon, 21 Nov 2011 23:55:59 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux i686; rv:7.0) Gecko/20110927 Thunderbird/7.0 MIME-Version: 1.0 To: Tejun Heo CC: "Rafael J. Wysocki" , pavel@ucw.cz, lenb@kernel.org, ak@linux.intel.com, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-mm@kvack.org, Chen Gong Subject: Re: [PATCH v4] PM / Memory-hotplug: Avoid task freezing failures References: <20111117083042.11419.19871.stgit@srivatsabhat.in.ibm.com> <201111192257.19763.rjw@sisk.pl> <4EC8984E.30005@linux.vnet.ibm.com> <201111201124.17528.rjw@sisk.pl> <4EC9D557.9090008@linux.vnet.ibm.com> <20111121164006.GB15314@google.com> <4ECA84A8.5030005@linux.vnet.ibm.com> <4ECA94A6.90500@linux.vnet.ibm.com> <20111121182319.GG15314@google.com> In-Reply-To: <20111121182319.GG15314@google.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit x-cbid: 11112108-6102-0000-0000-000000364C0B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/21/2011 11:53 PM, Tejun Heo wrote: > On Mon, Nov 21, 2011 at 11:42:54PM +0530, Srivatsa S. Bhat wrote: >> The lock_system_sleep() function is used in the memory hotplug code at >> several places in order to implement mutual exclusion with hibernation. >> However, this function tries to acquire the 'pm_mutex' lock using >> mutex_lock() and hence blocks in TASK_UNINTERRUPTIBLE state if it doesn't >> get the lock. This would lead to task freezing failures and hence >> hibernation failure as a consequence, even though the hibernation call path >> successfully acquired the lock. >> >> But it is to be noted that, since this task tries to acquire pm_mutex, if it >> blocks due to this, we are *100% sure* that this task is not going to run >> as long as hibernation sequence is in progress, since hibernation releases >> 'pm_mutex' only at the very end, when everything is done. >> And this means, this task is going to be anyway blocked for much more longer >> than what the freezer intends to achieve; which means, freezing and thawing >> doesn't really make any difference to this task! >> >> So, to fix freezing failures, we just ask the freezer to skip freezing this >> task, since it is already "frozen enough". >> >> But instead of calling freezer_do_not_count() and freezer_count() as it is, >> we use only the relevant parts of those functions, because restrictions >> such as 'the task should be a userspace one' etc., might not be relevant in >> this scenario. >> >> v4: Redesigned the whole fix, to ask the freezer to skip freezing the task >> which is blocked trying to acquire 'pm_mutex' lock. >> >> v3: Tejun suggested avoiding busy-looping by adding an msleep() since >> it is not guaranteed that we will get frozen immediately. >> >> v2: Tejun pointed problems with using mutex_lock_interruptible() in a >> while loop, when signals not related to freezing are involved. >> So, replaced it with mutex_trylock(). >> >> Signed-off-by: Srivatsa S. Bhat > > Acked-by: Tejun Heo > > Thanks a lot. :) > Thank you too :-) Regards, Srivatsa S. Bhat