From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752167AbaB1UeP (ORCPT ); Fri, 28 Feb 2014 15:34:15 -0500 Received: from e39.co.us.ibm.com ([32.97.110.160]:36315 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752125AbaB1UeK (ORCPT ); Fri, 28 Feb 2014 15:34:10 -0500 Date: Fri, 28 Feb 2014 12:34:05 -0800 From: "Paul E. McKenney" To: Vince Weaver Cc: "H. Peter Anvin" , Steven Rostedt , Peter Zijlstra , Linux Kernel , Ingo Molnar Subject: Re: perf_fuzzer compiled for x32 causes reboot Message-ID: <20140228203405.GH11910@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140225094352.73e0e28c@gandalf.local.home> <20140227173150.4e5ed747@gandalf.local.home> <530FC1C6.5040209@zytor.com> <20140227183008.6be081b7@gandalf.local.home> <530FCE6C.4080808@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14022820-9332-0000-0000-000003427E1F Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 27, 2014 at 08:00:04PM -0500, Vince Weaver wrote: > On Thu, 27 Feb 2014, H. Peter Anvin wrote: > > > On 02/27/2014 03:30 PM, Steven Rostedt wrote: > > > On Thu, 27 Feb 2014 14:52:54 -0800 > > > "H. Peter Anvin" wrote: > > > > > >> On 02/27/2014 02:31 PM, Steven Rostedt wrote: > > >>> > > >>> Yeah, something is getting mesed up. > > >>> > > >> > > >> What it *looks* like to me is that we try to nest the cr2 save/restore, > > >> which doesn't nest because it is a percpu variable. > > >> > > >> ... except in the x86-64 case, we *ALSO* save/restore cr2 inside > > >> entry_64.S, which makes the stuff in do_nmi completely redundant and > > >> there for no good reason. > > > > > > Peter, look at the code. That percpu cr2 is in a #ifdef CONFIG_X86_32 > > > section. That is, it isn't even executed. That's i386 code. The only > > > place the cr2 is saved for x86_64 is in entry_64.S. > > > > > > > Right, egg on my face. However, I still think it would make more sense > > for it to nest the way entry_64.S does if at all possible. > > > > That makes this even more confusing, though. I would still like to see > > what happens with the patch I sent Vince. > > I'll try your patch momentarily, first I had some other changes I started > running before I left work (for some reason it recompiled the whole > kernel). > > 8: function: perf_output_begin > 8: bprint: perf_output_begin: VMW: event type 2 config 2a st: 2c3e > 8: bputs: perf_output_begin: VMW: before rcu_dereference > 9: function: __do_page_fault > 9: function: down_read_trylock > 9: function: _cond_resched > 9: function: find_vma > > so it looks like the fault happens > > rcu_read_lock(); > > 116 /* > 117 * For inherited events we send all the output towards the parent. > 118 */ > 119 if (event->parent) > 120 event = event->parent; > 121 > > somewhere between here > > 122 rb = rcu_dereference(event->rb); > 123 if (unlikely(!rb)) > 124 goto out; > > and here > > 125 > 126 if (unlikely(!rb->nr_pages)) > 127 goto out; > > although if rcu locks do anything to turn off tracing then this could be > suspect. The most likely suspect is of course event->rb in the rcu_dereference. I have to defer to Steven on how rcu_read_lock() and rcu_read_unlock() currently interact with tracing. ;-) Thanx, Paul