Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932895Ab2HIOFP (ORCPT ); Thu, 9 Aug 2012 10:05:15 -0400 Received: from mail-lpp01m010-f46.google.com ([209.85.215.46]:45158 "EHLO mail-lpp01m010-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932626Ab2HIOFL (ORCPT ); Thu, 9 Aug 2012 10:05:11 -0400 MIME-Version: 1.0 In-Reply-To: <50235ED0.5010107@intel.com> References: <50235ED0.5010107@intel.com> Date: Thu, 9 Aug 2012 16:05:09 +0200 Message-ID: Subject: Re: [BUG] perf: sharing of cpuctx between core and ibs PMU causes problems From: Stephane Eranian To: "Yan, Zheng" Cc: LKML , Peter Zijlstra , Robert Richter , mingo@elte.hu Content-Type: text/plain; charset=UTF-8 X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1604 Lines: 42 On Thu, Aug 9, 2012 at 8:55 AM, Yan, Zheng wrote: > 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. > Well, but then you're doing the same work twice. >> >> 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. > Yes, I think IBS should do the same and that should fix the problem there too. Will try that. -- 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/