From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756698Ab0BEJqE (ORCPT ); Fri, 5 Feb 2010 04:46:04 -0500 Received: from mx1.redhat.com ([209.132.183.28]:15363 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751918Ab0BEJqB (ORCPT ); Fri, 5 Feb 2010 04:46:01 -0500 Message-ID: <4B6BE966.8010006@redhat.com> Date: Fri, 05 Feb 2010 17:48:22 +0800 From: Cong Wang User-Agent: Thunderbird 2.0.0.23 (X11/20091001) MIME-Version: 1.0 To: "Eric W. Biederman" CC: Xiaotian Feng , linux-kernel@vger.kernel.org, Tejun Heo , Greg Kroah-Hartman , Peter Zijlstra , Miles Lane , Heiko Carstens , Benjamin Herrenschmidt , Larry Finger , akpm@linux-foundation.org, Jens Axboe Subject: Re: [Patch v2] sysfs: add lockdep class support to s_active References: <20100205064622.4141.72867.sendpatchset@localhost.localdomain> <7b6bb4a51002042309v3ca1dd0p60b9dbcacdafaee6@mail.gmail.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Eric W. Biederman wrote: > Xiaotian Feng writes: > >> On Fri, Feb 5, 2010 at 2:42 PM, Amerigo Wang wrote: >>> Recently we met a lockdep warning from sysfs during s2ram or cpu hotplug. >>> As reported by several people, it is something like: >>> >>> [ 6967.926563] ACPI: Preparing to enter system sleep state S3 >>> [ 6967.956156] Disabling non-boot CPUs ... >>> [ 6967.970401] >>> [ 6967.970408] ============================================= >>> [ 6967.970419] [ INFO: possible recursive locking detected ] >>> [ 6967.970431] 2.6.33-rc2-git6 #27 >>> [ 6967.970439] --------------------------------------------- >>> [ 6967.970450] pm-suspend/22147 is trying to acquire lock: >>> [ 6967.970460] (s_active){++++.+}, at: [] >>> sysfs_hash_and_remove+0x3d/0x4f >>> [ 6967.970493] >>> [ 6967.970497] but task is already holding lock: >>> [ 6967.970506] (s_active){++++.+}, at: [] >>> sysfs_get_active_two+0x16/0x36 >>> [...] >>> >>> Eric already provides a patch for this[1], but it still can't fix the >>> problem. Based on his work and Peter's suggestion, I write this patch, >>> hopefully we can fix the warning completely. >>> >>> This patch put sysfs s_active into two classes, one is for PM, the other >>> is for the rest, so lockdep will distinguish them. >> I think this patch does not hit the root cause, we have a similiar >> warning which is not related with PM. > > The root cause is that our locking is crazy complicated. No lockdep > changes are going to fix that. > > What we can do and what the patch does is teach lockdep to treat some > of the sysfs files as a different group (subclass) from other sysfs > files. Which keeps us from overgeneralizing too much and having > a better signal to noise ratio. > > As for the block device problem goes, I can't easily say that > the block layer is correct. I expect it is because changing > the scheduler is unlikely to delete block devices. If the block layer > has bugs then adding another subclass as Amerigo suggests should simply > make lockdep warnings harder to trigger and more accurate so that > sounds like a path worth walking. > > In general I recommend that pieces of code that need to do a lot of > work in a sysfs attribute consider using a work queue or a kernel > thread, as that can be easier to analyze. > Cc'ing Jens Axboe.