Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965137Ab3GLRDu (ORCPT ); Fri, 12 Jul 2013 13:03:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:15418 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965101Ab3GLRDt (ORCPT ); Fri, 12 Jul 2013 13:03:49 -0400 Date: Fri, 12 Jul 2013 13:00:18 -0400 From: Dave Jones To: Dave Hansen Cc: Dave Hansen , Ingo Molnar , Markus Trippelsdorf , Thomas Gleixner , Linus Torvalds , Linux Kernel , Peter Anvin , Peter Zijlstra , Dave Hansen Subject: Re: Yet more softlockups. Message-ID: <20130712170018.GA1537@redhat.com> Mail-Followup-To: Dave Jones , Dave Hansen , Dave Hansen , Ingo Molnar , Markus Trippelsdorf , Thomas Gleixner , Linus Torvalds , Linux Kernel , Peter Anvin , Peter Zijlstra , Dave Hansen References: <20130705160043.GF325@redhat.com> <20130706072408.GA14865@gmail.com> <20130710151324.GA11309@redhat.com> <20130710152015.GA757@x4> <20130710154029.GB11309@redhat.com> <20130712103117.GA14862@gmail.com> <51E0230C.9010509@intel.com> <20130712154521.GD1020@redhat.com> <51E026F3.6010505@sr71.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51E026F3.6010505@sr71.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1656 Lines: 39 On Fri, Jul 12, 2013 at 08:55:31AM -0700, Dave Hansen wrote: > I mean that somebody turned 'active_events' on without actually wanting > perf to be on. I'd be curious how it got set to something nonzero. > Could you stick a WARN_ONCE() or printk_ratelimit() on the three sites > that modify it? I'll add to my list of things to get to, but it probably won't be until post-weekend. > > Here's a fun trick: > > > > trinity -c perf_event_open -C4 -q -l off > > > > Within about a minute, that brings any of my boxes to its knees. > > The softlockup detector starts going nuts, and then the box wedges solid. > > *But* dropping the perf sample rate has been really effective at keeping > me from hitting it, and I've had to use _lots_ of CPUs (60-160) doing > those NMIs at once to trigger the lockups. > > Being able to trigger it with so few CPUs is interesting though. I'll > try on my hardware. I hacked trinity to pause for 24s after each call, and changed the kernel to taint on lockup (so that trinity would immediatly stop). My hope was to find the combination of perf_event_open calls that triggered this. After 12 hours, it's still ticking along. It's now done about a thousand more calls than is usually necessary to hit the bug. Which makes me wonder if this is timing related somehow. Perhaps also worth noting that the majority of calls trinity makes will -EINVAL Dave -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/