From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta8.messagelabs.com (mail6.bemta8.messagelabs.com [216.82.243.55]) by kanga.kvack.org (Postfix) with ESMTP id 07BC26B006E for ; Mon, 21 Nov 2011 13:23:26 -0500 (EST) Received: by vbbfq11 with SMTP id fq11so3662118vbb.14 for ; Mon, 21 Nov 2011 10:23:25 -0800 (PST) Date: Mon, 21 Nov 2011 10:23:19 -0800 From: Tejun Heo Subject: Re: [PATCH v4] PM / Memory-hotplug: Avoid task freezing failures Message-ID: <20111121182319.GG15314@google.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4ECA94A6.90500@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Srivatsa S. Bhat" 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 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. :) -- tejun -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org