Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759217AbcJTJnE (ORCPT ); Thu, 20 Oct 2016 05:43:04 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36570 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754963AbcJTJnC (ORCPT ); Thu, 20 Oct 2016 05:43:02 -0400 Date: Thu, 20 Oct 2016 11:42:59 +0200 From: Jiri Olsa To: Peter Zijlstra 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: <20161020094259.GA14853@krava> 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> <20161020090416.GS3102@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161020090416.GS3102@twins.programming.kicks-ass.net> User-Agent: Mutt/1.7.1 (2016-10-04) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Thu, 20 Oct 2016 09:43:01 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1530 Lines: 56 On Thu, Oct 20, 2016 at 11:04:16AM +0200, Peter Zijlstra wrote: > 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 */ ah, I thought this part would add the device back.. but it's already out of the pmu list.. right :-\ thanks, jirka > /* 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.