Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755409Ab2HIGzQ (ORCPT ); Thu, 9 Aug 2012 02:55:16 -0400 Received: from mga11.intel.com ([192.55.52.93]:36938 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755149Ab2HIGzO (ORCPT ); Thu, 9 Aug 2012 02:55:14 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.77,738,1336374000"; d="scan'208";a="205333400" Message-ID: <50235ED0.5010107@intel.com> Date: Thu, 09 Aug 2012 14:55:12 +0800 From: "Yan, Zheng" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Stephane Eranian CC: LKML , Peter Zijlstra , Robert Richter , mingo@elte.hu Subject: Re: [BUG] perf: sharing of cpuctx between core and ibs PMU causes problems References: In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1591 Lines: 52 On 08/09/2012 08:51 AM, Stephane Eranian wrote: > Hi, > > I ran into a problem on my AMD box whereby I would hit the > WARN_ON_ONCE(cpuctx->cgrp) in perf_cgroup_switch(). > > It took me a while to track this down. It turns out that the > list_for_each_entry_rcu() loop had multiple iterations. That's > normal, we have CPU PMU and IBS PMU. But what caused > the warning to fire is that both the core and IBS PMU were > pointing to the same cpuctx struct. Thus, the cpuctx->cgrp > was already set in the second iteration. > > Is the warning a false positive? I think it's a false positive, I'm not sure. > > In perf_pmu_register(), there is a search for a matching > pmu->task_ctx_nr. Given that the field is pointing to > perf_hw_context for both cpu and IBS PMU, there is > a match and therefore the cpuctx are shared. > > The question is: why do we have to share the cpuctx? > > Note that the same issue probably exists with the Intel > uncore PMU. uncore PMU does not have this issue because uncore_pmu->task_ctx_nr is 'perf_invalid_context'. find_pmu_context() always return NULL in that case. Regards Yan, Zheng. > > If we need to share, then the perf_cgroup_switch() code > needs to change because, as it stands, it is doing the > switching twice in this case. > > Either way something looks wrong here. > > Any idea? > -- 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/