From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932654AbcJTFjt (ORCPT ); Thu, 20 Oct 2016 01:39:49 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:34425 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752278AbcJTFjs (ORCPT ); Thu, 20 Oct 2016 01:39:48 -0400 Date: Thu, 20 Oct 2016 07:39:44 +0200 From: Peter Zijlstra To: Jiri Olsa Cc: CAI Qian , Rob Herring , Kan Liang , Greg Kroah-Hartman , linux-kernel , Ingo Molnar Subject: Re: [4.9-rc1+] intel_uncore builtin + CONFIG_DEBUG_TEST_DRIVER_REMOVE kernel panic Message-ID: <20161020053944.GQ3102@twins.programming.kicks-ass.net> References: <907882571.66590.1476113724660.JavaMail.zimbra@redhat.com> <1219480016.67057.1476113847440.JavaMail.zimbra@redhat.com> <20161010172023.GA7148@kroah.com> <1035662571.647973.1476888331396.JavaMail.zimbra@redhat.com> <20161019191943.GA7951@krava> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161019191943.GA7951@krava> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 19, 2016 at 09:19:43PM +0200, Jiri Olsa wrote: > I think the reason here is that presume pmu devices are always added, > but we add them only if pmu_bus_running (in perf_event_sysfs_init) > is set which might happen after uncore initcall > > attached patch fixes the issue for me Right, we never expected to be unloaded before userspace runs. Strictly speaking we should only read pmu_bus_running while holding pmus_lock, that way we're serialized against perf_event_sysfs_init() flipping it while we're being removed etc.. With the current setup the introduced race is harmless, but who knows what other crazy these device people will come up with ;-) > --- > diff --git a/kernel/events/core.c b/kernel/events/core.c > index c6e47e97b33f..c2099b799d16 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -8871,8 +8871,10 @@ void perf_pmu_unregister(struct pmu *pmu) > idr_remove(&pmu_idr, pmu->type); > if (pmu->nr_addr_filters) > device_remove_file(pmu->dev, &dev_attr_nr_addr_filters); > - device_del(pmu->dev); > - put_device(pmu->dev); > + if (pmu_bus_running) { > + device_del(pmu->dev); > + put_device(pmu->dev); > + } > free_pmu_context(pmu); > } > EXPORT_SYMBOL_GPL(perf_pmu_unregister);