From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932724AbdJaUMP (ORCPT ); Tue, 31 Oct 2017 16:12:15 -0400 Received: from mail-pg0-f46.google.com ([74.125.83.46]:53799 "EHLO mail-pg0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752066AbdJaUMM (ORCPT ); Tue, 31 Oct 2017 16:12:12 -0400 X-Google-Smtp-Source: ABhQp+QFRKbGQq2SaFVhauO12hiRcHv2DwjvqWHJ+pPD1BMS9SsWasVEMCbGuycqZKhmX1yexEj0eg== Date: Tue, 31 Oct 2017 13:12:08 -0700 From: Guenter Roeck To: Don Zickus Cc: Peter Zijlstra , Thomas Gleixner , linux-kernel@vger.kernel.org, Ingo Molnar Subject: Re: Crashes in perf_event_ctx_lock_nested Message-ID: <20171031201208.GA23413@roeck-us.net> References: <20171030224512.GA13592@roeck-us.net> <20171031134850.ynix2zqypmca2mtt@hirez.programming.kicks-ass.net> <20171031171622.GA28688@roeck-us.net> <20171031185059.2yl4qrxvrqqzra3d@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171031185059.2yl4qrxvrqqzra3d@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 31, 2017 at 02:50:59PM -0400, Don Zickus wrote: > On Tue, Oct 31, 2017 at 10:16:22AM -0700, Guenter Roeck wrote: > > On Tue, Oct 31, 2017 at 02:48:50PM +0100, Peter Zijlstra wrote: > > > On Mon, Oct 30, 2017 at 03:45:12PM -0700, Guenter Roeck wrote: > > > > I added some logging and a long msleep() in hardlockup_detector_perf_cleanup(). > > > > Here is the result: > > > > > > > > [ 0.274361] NMI watchdog: ############ hardlockup_detector_perf_init > > > > [ 0.274915] NMI watchdog: ############ hardlockup_detector_event_create(0) > > > > [ 0.277049] NMI watchdog: ############ hardlockup_detector_perf_cleanup > > > > [ 0.277593] NMI watchdog: ############ hardlockup_detector_perf_enable(0) > > > > [ 0.278027] NMI watchdog: ############ hardlockup_detector_event_create(0) > > > > [ 1.312044] NMI watchdog: ############ hardlockup_detector_perf_cleanup done > > > > [ 1.385122] NMI watchdog: ############ hardlockup_detector_perf_enable(1) > > > > [ 1.386028] NMI watchdog: ############ hardlockup_detector_event_create(1) > > > > [ 1.466102] NMI watchdog: ############ hardlockup_detector_perf_enable(2) > > > > [ 1.475536] NMI watchdog: ############ hardlockup_detector_event_create(2) > > > > [ 1.535099] NMI watchdog: ############ hardlockup_detector_perf_enable(3) > > > > [ 1.535101] NMI watchdog: ############ hardlockup_detector_event_create(3) > > > > > > > [ 7.222816] NMI watchdog: ############ hardlockup_detector_perf_disable(0) > > > > [ 7.230567] NMI watchdog: ############ hardlockup_detector_perf_disable(1) > > > > [ 7.243138] NMI watchdog: ############ hardlockup_detector_perf_disable(2) > > > > [ 7.250966] NMI watchdog: ############ hardlockup_detector_perf_disable(3) > > > > [ 7.258826] NMI watchdog: ############ hardlockup_detector_perf_enable(1) > > > > [ 7.258827] NMI watchdog: ############ hardlockup_detector_perf_cleanup > > > > [ 7.258831] NMI watchdog: ############ hardlockup_detector_perf_enable(2) > > > > [ 7.258833] NMI watchdog: ############ hardlockup_detector_perf_enable(0) > > > > [ 7.258834] NMI watchdog: ############ hardlockup_detector_event_create(2) > > > > [ 7.258835] NMI watchdog: ############ hardlockup_detector_event_create(0) > > > > [ 7.260169] NMI watchdog: ############ hardlockup_detector_perf_enable(3) > > > > [ 7.260170] NMI watchdog: ############ hardlockup_detector_event_create(3) > > > > [ 7.494251] NMI watchdog: ############ hardlockup_detector_event_create(1) > > > > [ 8.287135] NMI watchdog: ############ hardlockup_detector_perf_cleanup done > > > > > > > > Looks like there are a number of problems: hardlockup_detector_event_create() > > > > creates the event data structure even if it is already created, > > > > > > Right, that does look dodgy. And on its own should be fairly straight > > > forward to cure. But I'd like to understand the rest of it first. > > > > > > > and hardlockup_detector_perf_cleanup() runs unprotected and in > > > > parallel to the enable/create functions. > > > > > > Well, looking at the code, cpu_maps_update_begin() aka. > > > cpu_add_remove_lock is serializing cpu_up() and cpu_down() and _should_ > > > thereby also serialize cleanup vs the smp_hotplug_thread operations. > > > > > > Your trace does indeed indicate this is not the case, but I cannot, from > > > the code, see how this could happen. > > > > > > Could you use trace_printk() instead and boot with > > > "trace_options=stacktrace" ? > > > > > Attached. Let me know if you need more information. Note this is with > > msleep(1000) in the cleanup function to avoid the crash. > > > > > > ALso, the following message is seen twice. > > > > > > > > [ 0.278758] NMI watchdog: Enabled. Permanently consumes one hw-PMU counter. > > > > [ 7.258838] NMI watchdog: Enabled. Permanently consumes one hw-PMU counter. > > > > > > > > I don't offer a proposed patch since I have no idea how to best solve the > > > > problem. > > > > > > > > Also, is the repeated enable/disable/cleanup as part of the normal boot > > > > really necessary ? > > > > > > That's weird, I don't see that on my machines. We very much only bring > > > up the CPUs _once_. Also note they're 7s apart. Did you do something > > > funny like resume-from-disk or so? > > > > No, just whatever Chrome OS does when it starts the kernel. The hardware > > used in this test is a Google Pixelbook, though we have also seen the problem > > with other Chromebooks. > > Is Chrome OS, changing the default timeout from 10s to something else? > That would explain it as a script is executed late in the boot cycle and > explain the quick restart. > Correct, Chrome OS changes the timeout from 10 to 5 seconds. A little experiment suggests that the problem can be triggered by updating /proc/sys/kernel/watchdog_thresh. hardlockup_detector_perf_enable() is called while hardlockup_detector_perf_cleanup() is running. Guenter