Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756712AbcJTJEY (ORCPT ); Thu, 20 Oct 2016 05:04:24 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:33469 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750853AbcJTJEU (ORCPT ); Thu, 20 Oct 2016 05:04:20 -0400 Date: Thu, 20 Oct 2016 11:04:16 +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: <20161020090416.GS3102@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> <20161020053944.GQ3102@twins.programming.kicks-ass.net> <20161020085803.GA31721@krava> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161020085803.GA31721@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 Content-Length: 1252 Lines: 48 On Thu, Oct 20, 2016 at 10:58:03AM +0200, Jiri Olsa wrote: > @@ -8869,11 +8869,15 @@ void perf_pmu_unregister(struct pmu *pmu) > free_percpu(pmu->pmu_disable_count); > if (pmu->type >= PERF_TYPE_MAX) > 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); > + mutex_lock(&pmus_lock); > + if (pmu_bus_running) { > + if (pmu->nr_addr_filters) > + device_remove_file(pmu->dev, &dev_attr_nr_addr_filters); > + device_del(pmu->dev); > + put_device(pmu->dev); > + } > free_pmu_context(pmu); > + mutex_unlock(&pmus_lock); > } > EXPORT_SYMBOL_GPL(perf_pmu_unregister); I think that is still racy.. unregister: sysfs_init: mutex_lock(&pmus_lock); list_del_rcu(&pmu->entry); mutex_unlock(&pmus_lock); synchronize_*rcu(); mutex_lock(&pmus_lock); list_for_each_entry(pmu, &pmus, entry) { /* add device muck */ /* will _NOT_ see our PMU */ } pmus_bus_running = 1; mutex_unlock(&pmus_lock); mutex_lock(&pmus_lock); if (pmu_bus_running) { device_del() /* OOPS */ What you want is to read pmu_bus_running in the same pmus_lock section as we do the list_del, and then use that local copy later.