From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753944AbbAWEG2 (ORCPT ); Thu, 22 Jan 2015 23:06:28 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:32148 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752017AbbAWEG0 (ORCPT ); Thu, 22 Jan 2015 23:06:26 -0500 Message-ID: <54C1C899.8000106@oracle.com> Date: Thu, 22 Jan 2015 23:05:45 -0500 From: Sasha Levin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: Lai Jiangshan , Ingo Molnar , Peter Zijlstra , LKML , "davej@codemonkey.org.uk >> Dave Jones" Subject: Re: rcu, sched: WARNING: CPU: 30 PID: 23771 at kernel/rcu/tree_plugin.h:337 rcu_read_unlock_special+0x369/0x550() References: <54BBC084.2030604@oracle.com> <20150118232255.GD9719@linux.vnet.ibm.com> <54BE76B9.7070907@oracle.com> <20150121025754.GV9719@linux.vnet.ibm.com> <54BFC979.8040107@oracle.com> <20150122004305.GJ9719@linux.vnet.ibm.com> <54C1BFFD.9060707@oracle.com> <20150123035158.GP9719@linux.vnet.ibm.com> <54C1C7D2.906@oracle.com> In-Reply-To: <54C1C7D2.906@oracle.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Source-IP: ucsinet22.oracle.com [156.151.31.94] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/22/2015 11:02 PM, Sasha Levin wrote: > On 01/22/2015 10:51 PM, Paul E. McKenney wrote: >> On Thu, Jan 22, 2015 at 10:29:01PM -0500, Sasha Levin wrote: >>>> On 01/21/2015 07:43 PM, Paul E. McKenney wrote: >>>>>> On Wed, Jan 21, 2015 at 10:44:57AM -0500, Sasha Levin wrote: >>>>>>>> On 01/20/2015 09:57 PM, Paul E. McKenney wrote: >>>>>>>>>>>>>> So RCU believes that an RCU read-side critical section that ended within >>>>>>>>>>>>>>>>>> an interrupt handler (in this case, an hrtimer) somehow got preempted. >>>>>>>>>>>>>>>>>> Which is not supposed to happen. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> Do you have CONFIG_PROVE_RCU enabled? If not, could you please enable it >>>>>>>>>>>>>>>>>> and retry? >>>>>>>>>>>>>> >>>>>>>>>>>>>> I did have CONFIG_PROVE_RCU, and didn't see anything else besides what I pasted here. >>>>>>>>>> OK, fair enough. I do have a stack of RCU CPU stall-warning changes on >>>>>>>>>> their way in, please see v3.19-rc1..630181c4a915 in -rcu, which is at: >>>>>>>>>> >>>>>>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git >>>>>>>>>> >>>>>>>>>> These handle the problems that Dave Jones, yourself, and a few others >>>>>>>>>> located this past December. Could you please give them a spin? >>>>>>>> >>>>>>>> They seem to be a part of -next already, so this testing already includes them. >>>>>>>> >>>>>>>> I seem to be getting them about once a day, anything I can add to debug it? >>>>>> >>>>>> Could you please try reproducing with the following patch? >>>> >>>> Yes, and I've got mixed results. It reproduced, and all I got was: >>>> >>>> [ 717.645572] =============================== >>>> [ 717.645572] [ INFO: suspicious RCU usage. ] >>>> [ 717.645572] 3.19.0-rc5-next-20150121-sasha-00064-g3c37e35-dirty #1809 Tainted: G W >>>> [ 717.645572] ------------------------------- >>>> [ 717.645572] kernel/rcu/tree_plugin.h:337 rcu_read_unlock() from irq or softirq with blocking in critical section!!! >>>> [ 717.645572] ! >>>> [ 717.645572] >>>> [ 717.645572] other info that might help us debug this: >>>> [ 717.645572] >>>> [ 717.645572] >>>> [ 717.645572] rcu_scheduler_active = 1, debug_locks = 1 >>>> [ 717.645572] 3 locks held by trinity-c29/16497: >>>> [ 717.645572] #0: (&sb->s_type->i_mutex_key){+.+.+.}, at: [] lookup_slow+0xd3/0x420 >>>> [ 717.645572] #1: >>>> [hang] >>>> >>>> So the rest of the locks/stack trace didn't get printed, nor the pr_alert() which >>>> should follow that. >>>> >>>> I've removed the lockdep call and will re-run it. >> Thank you! You are keeping the pr_alert(), correct? > > Yup, just the lockdep call goes away. Okay, this reproduced faster than I anticipated: [ 786.160131] ->rcu_read_unlock_special: 0x100 (b: 0, nq: 1) [ 786.239513] ->rcu_read_unlock_special: 0x100 (b: 0, nq: 1) [ 786.240503] ->rcu_read_unlock_special: 0x100 (b: 0, nq: 1) [ 786.242575] ->rcu_read_unlock_special: 0x100 (b: 0, nq: 1) [ 786.243565] ->rcu_read_unlock_special: 0x100 (b: 0, nq: 1) [ 786.243565] ->rcu_read_unlock_special: 0x100 (b: 0, nq: 1) [ 786.243565] ->rcu_read_unlock_special: 0x100 (b: 0, nq: 1) [ 786.243565] ->rcu_read_unlock_special: 0x100 (b: 0, nq: 1) [ 786.243565] ->rcu_read_unlock_special: 0x100 (b: 0, nq: 1) It seems like the WARN_ON_ONCE was hiding the fact it actually got hit couple of times in a very short interval. Maybe that would also explain lockdep crapping itself. Thanks, Sasha