From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755983AbbAaB3r (ORCPT ); Fri, 30 Jan 2015 20:29:47 -0500 Received: from userp1040.oracle.com ([156.151.31.81]:33921 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752290AbbAaB3o (ORCPT ); Fri, 30 Jan 2015 20:29:44 -0500 Message-ID: <54CC2FA8.7070006@oracle.com> Date: Fri, 30 Jan 2015 20:28:08 -0500 From: Sasha Levin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Andy Lutomirski , Paul McKenney CC: Borislav Petkov , X86 ML , Linus Torvalds , "linux-kernel@vger.kernel.org" , Peter Zijlstra , Oleg Nesterov , Tony Luck , Andi Kleen , Josh Triplett , =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVj?= =?UTF-8?B?a2Vy?= Subject: Re: [PATCH v4 2/5] x86, traps: Track entry into and exit from IST context References: <7665538633a500255d7da9ca5985547f6a2aa191.1416604491.git.luto@amacapital.net> <54C17139.1040706@oracle.com> <20150123180455.GA3192@pd.tnic> <54C2B396.9090106@oracle.com> <20150128174817.GQ19109@linux.vnet.ibm.com> <54CBE23F.3010003@oracle.com> In-Reply-To: <54CBE23F.3010003@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Source-IP: ucsinet21.oracle.com [156.151.31.93] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/30/2015 02:57 PM, Sasha Levin wrote: > On 01/28/2015 04:02 PM, Andy Lutomirski wrote: >> On Wed, Jan 28, 2015 at 9:48 AM, Paul E. McKenney >> wrote: >>> On Wed, Jan 28, 2015 at 08:33:06AM -0800, Andy Lutomirski wrote: >>>> On Fri, Jan 23, 2015 at 5:25 PM, Andy Lutomirski wrote: >>>>> On Fri, Jan 23, 2015 at 12:48 PM, Sasha Levin wrote: >>>>>> On 01/23/2015 01:34 PM, Andy Lutomirski wrote: >>>>>>> On Fri, Jan 23, 2015 at 10:04 AM, Borislav Petkov wrote: >>>>>>>> On Fri, Jan 23, 2015 at 09:58:01AM -0800, Andy Lutomirski wrote: >>>>>>>>>> [ 543.999079] Call Trace: >>>>>>>>>> [ 543.999079] dump_stack (lib/dump_stack.c:52) >>>>>>>>>> [ 543.999079] lockdep_rcu_suspicious (kernel/locking/lockdep.c:4259) >>>>>>>>>> [ 543.999079] atomic_notifier_call_chain (include/linux/rcupdate.h:892 kernel/notifier.c:182 kernel/notifier.c:193) >>>>>>>>>> [ 543.999079] ? atomic_notifier_call_chain (kernel/notifier.c:192) >>>>>>>>>> [ 543.999079] notify_die (kernel/notifier.c:538) >>>>>>>>>> [ 543.999079] ? atomic_notifier_call_chain (kernel/notifier.c:538) >>>>>>>>>> [ 543.999079] ? debug_smp_processor_id (lib/smp_processor_id.c:57) >>>>>>>>>> [ 543.999079] do_debug (arch/x86/kernel/traps.c:652) >>>>>>>>>> [ 543.999079] ? trace_hardirqs_on (kernel/locking/lockdep.c:2609) >>>>>>>>>> [ 543.999079] ? do_int3 (arch/x86/kernel/traps.c:610) >>>>>>>>>> [ 543.999079] ? trace_hardirqs_on_caller (kernel/locking/lockdep.c:2554 kernel/locking/lockdep.c:2601) >>>>>>>>>> [ 543.999079] debug (arch/x86/kernel/entry_64.S:1310) >>>>>>>>> >>>>>>>>> I don't know how to read this stack trace. Are we in do_int3, >>>>>>>>> do_debug, or both? I didn't change do_debug at all. >>>>>>>> >>>>>>>> It looks like we're in do_debug. do_int3 is only on the stack but not >>>>>>>> part of the current frame if I can trust the '?' ... >>>>>>>> >>>>>>> >>>>>>> It's possible that an int3 happened and I did something wrong on >>>>>>> return that caused a subsequent do_debug to screw up, but I don't see >>>>>>> how my patch would have caused that. >>>>>>> >>>>>>> Were there any earlier log messages? >>>>>> >>>>>> Nope, nothing odd before or after. >>>>> >>>>> Trinity just survived for a decent amount of time for me with my >>>>> patches, other than a bunch of apparently expected OOM kills. I have >>>>> no idea how to tell trinity how much memory to use. >>>> >>>> A longer trinity run on a larger VM survived (still with some OOM >>>> kills, but no taint) with these patches. I suspect that it's a >>>> regression somewhere else in the RCU changes. I have >>>> CONFIG_PROVE_RCU=y, so I should have seen the failure if it was there, >>>> I think. >>> >>> If by "RCU changes" you mean my changes to the RCU infrastructure, I am >>> going to need more of a hint than I see in this thread thus far. ;-) >>> >> >> I can't help much, since I can't reproduce the problem. Presumably if >> it's a bug in -tip, someone else will trigger it, too. > > I'm not sure what to tell you here, I'm not using any weird options for trinity > to reproduce it. > > It doesn't happen to frequently, but I still see it happening. > > Would you like me to try a debug patch or something similar? After talking with Paul we know what's going on here: do_debug() calls ist_enter() to indicate we're running on the interrupt stack. The first think ist_enter() does is: preempt_count_add(HARDIRQ_OFFSET); After this, as far as the kernel is concerned, we're in interrupt mode so in_interrupt() will return true. Next, we'll call exception_enter() which won't do anything since: void context_tracking_user_exit(void) { unsigned long flags; if (!context_tracking_is_enabled()) return; if (in_interrupt()) <=== This returns true, so nothing else gets done return; At this stage we never tell RCU that we exited user mode, but then we try to use it calling the notifiers, which explains the warnings I'm seeing. Thanks, Sasha