From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751638AbaB1A6A (ORCPT ); Thu, 27 Feb 2014 19:58:00 -0500 Received: from mail-qg0-f42.google.com ([209.85.192.42]:57291 "EHLO mail-qg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751003AbaB1A56 (ORCPT ); Thu, 27 Feb 2014 19:57:58 -0500 Date: Thu, 27 Feb 2014 20:00:04 -0500 (EST) From: Vince Weaver To: "H. Peter Anvin" cc: Steven Rostedt , Vince Weaver , Peter Zijlstra , Linux Kernel , Ingo Molnar Subject: Re: perf_fuzzer compiled for x32 causes reboot In-Reply-To: <530FCE6C.4080808@zytor.com> Message-ID: References: <530B841F.5050803@zytor.com> <530B90A5.3090302@zytor.com> <20140224141329.1cd3bb52@gandalf.local.home> <20140224193043.GP6835@laptop.programming.kicks-ass.net> <530C12CA.6070308@zytor.com> <20140225094352.73e0e28c@gandalf.local.home> <20140227173150.4e5ed747@gandalf.local.home> <530FC1C6.5040209@zytor.com> <20140227183008.6be081b7@gandalf.local.home> <530FCE6C.4080808@zytor.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Vince