From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755748Ab1JXLsj (ORCPT ); Mon, 24 Oct 2011 07:48:39 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:45167 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755452Ab1JXLsh (ORCPT ); Mon, 24 Oct 2011 07:48:37 -0400 Date: Mon, 24 Oct 2011 04:48:06 -0700 From: "Paul E. McKenney" To: Ingo Molnar Cc: eric.dumazet@gmail.com, shaohua.li@intel.com, ak@linux.intel.com, mhocko@suse.cz, alex.shi@intel.com, efault@gmx.de, linux-kernel@vger.kernel.org Subject: Re: [GIT PULL rcu/next] RCU commits for 3.1 Message-ID: <20111024114806.GA3340@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110930204503.GA32687@linux.vnet.ibm.com> <20111001152514.GA16930@elte.hu> <20111003055302.GA23527@elte.hu> <20111003161335.GA2403@linux.vnet.ibm.com> <20111004074637.GA14061@elte.hu> <20111024100501.GA24913@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111024100501.GA24913@linux.vnet.ibm.com> User-Agent: Mutt/1.5.20 (2009-06-14) x-cbid: 11102411-5930-0000-0000-00000087147A Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 24, 2011 at 03:05:01AM -0700, Paul E. McKenney wrote: > On Tue, Oct 04, 2011 at 09:46:37AM +0200, Ingo Molnar wrote: > > > > * Paul E. McKenney wrote: > > > > > On Mon, Oct 03, 2011 at 07:53:02AM +0200, Ingo Molnar wrote: > > > > > > > > Not sure whether you've seen this one already: > > > > > > This is a new one for me. > > > > > > > [ 18.110320] Adding 3911820k swap on /dev/sda2. Priority:-1 extents:1 across:3911820k > > > > [ 31.803721] > > > > [ 31.804597] =============================== > > > > [ 31.804597] [ INFO: suspicious RCU usage. ] > > > > [ 31.804597] ------------------------------- > > > > [ 31.804597] include/linux/cgroup.h:548 suspicious rcu_dereference_check() usage! > > > > [ 31.804597] > > > > [ 31.804597] other info that might help us debug this: > > > > [ 31.804597] > > > > [ 31.804597] > > > > [ 31.804597] rcu_scheduler_active = 1, debug_locks = 0 > > > > [ 31.804597] 1 lock held by true/845: > > > > [ 31.804597] #0: (&sig->cred_guard_mutex){+.+.+.}, at: [<4109f06f>] prepare_bprm_creds+0x20/0x55 > > > > [ 31.804597] > > > > [ 31.804597] stack backtrace: > > > > [ 31.804597] Pid: 845, comm: true Not tainted 3.1.0-rc8-tip-01699-gde204a2-dirty #157471 > > > > [ 31.804597] Call Trace: > > > > [ 31.804597] [<412d78fa>] ? printk+0x18/0x1a > > > > [ 31.804597] [<41044190>] lockdep_rcu_suspicious+0xb1/0xb9 > > > > [ 31.804597] [<4106d6de>] perf_event_comm+0xb1/0x357 > > > > [ 31.804597] [<4109f048>] set_task_comm+0x4d/0x54 > > > > > > This one does task_lock(), which acquires the task's > > > ->alloc lock. In theory, this should prevent the > > > lockdep-RCU splat. It clearly does not, and here are > > > some possible reasons why: > > > > > > 1. Something redirects to some other task along the way. > > > > > > 2. Something releases ->alloc_lock along the way. > > > > > > The output above shows no locks held, which points to #2. > > > > > > set_task_comm() calls perf_event_comm() shown above, which calls > > > perf_event_comm_event(), which does rcu_read_lock(), which should > > > also prevent the splat. Then perf_event_comm_event() calls > > > perf_event_comm_ctx(), which calls perf_event_comm_output()... > > > > > > Holy inlining, Batman!!! > > > > > > OK, I confess, I am a wuss... Any chance of reproducing this > > > with CONFIG_SCHED_OMIT_FRAME_POINTER=n? Or would someone more > > > familiar with these functions be willing to enlighten me? > > > > Ok, i ran the tests some more and here's a similar splat with > > framepointers enabled: > > > > [ 50.402719] eth0: no IPv6 routers present > > [ 59.147572] > > [ 59.149064] =============================== > > [ 59.151257] [ INFO: suspicious RCU usage. ] > > [ 59.156865] ------------------------------- > > [ 59.156865] include/linux/cgroup.h:548 suspicious rcu_dereference_check() usage! > > [ 59.156865] > > [ 59.156865] other info that might help us debug this: > > [ 59.156865] > > [ 59.156865] > > [ 59.156865] rcu_scheduler_active = 1, debug_locks = 0 > > [ 59.156865] 1 lock held by true/667: > > [ 59.156865] #0: (&sig->cred_guard_mutex){+.+.+.}, at: [] prepare_bprm_creds+0x27/0x70 > > [ 59.156865] > > [ 59.156865] stack backtrace: > > [ 59.156865] Pid: 667, comm: true Not tainted 3.1.0-rc8-tip+ #157499 > > [ 59.156865] Call Trace: > > [ 59.156865] [] ? printk+0x28/0x2a > > [ 59.156865] [] lockdep_rcu_suspicious+0xc0/0xd0 > > [ 59.156865] [] perf_event_enable_on_exec+0x1c8/0x1d0 > > [ 59.156865] [] ? __lock_release+0x54/0xd0 > > [ 59.156865] [] perf_event_comm+0x18/0x60 > > [ 59.156865] [] ? set_task_comm+0x5d/0x80 > > [ 59.156865] [] ? _raw_spin_unlock+0x1d/0x30 > > [ 59.156865] [] set_task_comm+0x64/0x80 > > [ 59.156865] [] setup_new_exec+0xc5/0x1f0 > > [ 59.156865] [] load_elf_binary+0x28b/0xa00 > > [ 59.156865] [] ? search_binary_handler+0xd9/0x1d0 > > [ 59.156865] [] ? __lock_release+0x54/0xd0 > > [ 59.156865] [] ? do_mmap+0x60/0x60 > > [ 59.156865] [] search_binary_handler+0xe0/0x1d0 > > [ 59.156865] [] ? search_binary_handler+0x30/0x1d0 > > [ 59.156865] [] do_execve_common+0x22f/0x2a0 > > [ 59.156865] [] do_execve+0x12/0x20 > > [ 59.156865] [] sys_execve+0x32/0x70 > > [ 59.156865] [] ptregs_execve+0x12/0x18 > > [ 59.156865] [] ? sysenter_do_call+0x12/0x36 > > > > Config and full bootlog attached. > > Hello, Ingo, > > It appears that inlining has defeated me, so I tried reproducing under > KVM, using the closest bootable approximation to your .config (attached). > I booted ten times without seeing this error. I have my changes against > 3.1-rc8. I will try against 3.1, but in the meantime any enlightenment > would be most welcome. ;-) And I cannot reproduce after merging into 3.1. :-( Thanx, Paul