From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756206Ab3AOCsF (ORCPT ); Mon, 14 Jan 2013 21:48:05 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:41232 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756137Ab3AOCsD (ORCPT ); Mon, 14 Jan 2013 21:48:03 -0500 Message-ID: <50F4C32E.4020509@oracle.com> Date: Mon, 14 Jan 2013 21:47:10 -0500 From: Sasha Levin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: Tejun Heo CC: Dave Jones , "linux-kernel@vger.kernel.org" Subject: cpuset: lockdep spew on proc_cpuset_show Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Source-IP: acsinet22.oracle.com [141.146.126.238] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Tejun, I've stumbled on the following: [ 75.972016] =============================== [ 75.977317] [ INFO: suspicious RCU usage. ] [ 76.041031] 3.8.0-rc3-next-20130114-sasha-00016-ga107525-dirty #262 Tainted: G W [ 76.057535] ------------------------------- [ 76.063397] include/linux/cgroup.h:534 suspicious rcu_dereference_check() usage! [ 76.076333] [ 76.076333] other info that might help us debug this: [ 76.076333] [ 76.087091] [ 76.087091] rcu_scheduler_active = 1, debug_locks = 1 [ 76.098682] 2 locks held by trinity/7514: [ 76.104154] #0: (&p->lock){+.+.+.}, at: [] seq_read+0x3a/0x3e0 [ 76.119533] #1: (cpuset_mutex){+.+...}, at: [] proc_cpuset_show+0x84/0x190 [ 76.151167] [ 76.151167] stack backtrace: [ 76.156853] Pid: 7514, comm: trinity Tainted: G W 3.8.0-rc3-next-20130114-sasha-00016-ga107525-dirty #262 [ 76.180547] Call Trace: [ 76.183754] [] lockdep_rcu_suspicious+0x10b/0x120 [ 76.191885] [] proc_cpuset_show+0x111/0x190 [ 76.200572] [] seq_read+0x1b7/0x3e0 [ 76.206843] [] ? seq_lseek+0x110/0x110 [ 76.213562] [] do_loop_readv_writev+0x4b/0x90 [ 76.220961] [] do_readv_writev+0xf6/0x1d0 [ 76.227940] [] vfs_readv+0x3e/0x60 [ 76.235971] [] sys_readv+0x50/0xd0 [ 76.241945] [] tracesys+0xe1/0xe6 This is the result of "cpuset: replace cgroup_mutex locking with cpuset internal locking" which remove the cgroup_lock() before calling task_subsys_state(), which now complains since one of the debug conditions in the rcu_dereference_check() there is cgroup_lock_is_held(). I'm not sure if this is an actual issue, but I do see that task_subsys_state() gets called from other places as well, so I think that possibly lockdep is right here and we do need to fix up locking there, but again, I'm not sure... Thanks, Sasha