From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758047Ab2F0XIa (ORCPT ); Wed, 27 Jun 2012 19:08:30 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:38828 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757462Ab2F0XI2 (ORCPT ); Wed, 27 Jun 2012 19:08:28 -0400 Date: Wed, 27 Jun 2012 16:08:23 -0700 From: Tejun Heo To: Glauber Costa Cc: Cgroups , linux-kernel Subject: Re: "Regression" with cd3d09527537 Message-ID: <20120627230823.GU15811@google.com> References: <4FE9AE57.4090007@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4FE9AE57.4090007@parallels.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 26, 2012 at 04:43:03PM +0400, Glauber Costa wrote: > Hi, > > I've recently started seeing a lockdep warning at the end of *every* > "init 0" issued in my machine. Actually, reboots are fine, and > that's probably why I've never seen it earlier. The log is quite > extensively, but shows the following dependency chain: > > [ 83.982111] -> #4 (cpu_hotplug.lock){+.+.+.}: > [...] > [ 83.982111] -> #3 (jump_label_mutex){+.+...}: > [...] > [ 83.982111] -> #2 (sk_lock-AF_INET){+.+.+.}: > [...] > [ 83.982111] -> #1 (&sig->cred_guard_mutex){+.+.+.}: > [...] > [ 83.982111] -> #0 (cgroup_mutex){+.+.+.}: > > I've recently fixed bugs with the lock ordering imposed by cpusets > on cpu_hotplug.lock through jump_label_mutex, and initially thought > it to be the same kind of issue. But that was not the case. > > I've omitted the full backtrace for readability, but I run this with > all cgroups disabled but the cpuset, so it can't be sock memcg > (after my initial reaction of "oh, fuck, not again"). That > jump_label is there for years, and it comes from the code that > disables socket timestamps. > (net_enable_timestamp) Yeah, there are multiple really large locks at play here - jump label, threadgroup and cgroup_mutex. It isn't pretty. Can you please post the full lockdep dump? The above only shows single locking chain. I'd like to see the other. Thanks. -- tejun