From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3y6RPg3wqPzDqln for ; Wed, 4 Oct 2017 17:51:03 +1100 (AEDT) Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v946ndTb043384 for ; Wed, 4 Oct 2017 02:51:01 -0400 Received: from e23smtp06.au.ibm.com (e23smtp06.au.ibm.com [202.81.31.148]) by mx0a-001b2d01.pphosted.com with ESMTP id 2dckeru4qu-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 04 Oct 2017 02:51:00 -0400 Received: from localhost by e23smtp06.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 4 Oct 2017 16:50:57 +1000 Received: from d23av02.au.ibm.com (d23av02.au.ibm.com [9.190.235.138]) by d23relay08.au.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id v946ou9J37879822 for ; Wed, 4 Oct 2017 17:50:56 +1100 Received: from d23av02.au.ibm.com (localhost [127.0.0.1]) by d23av02.au.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id v946oltt014350 for ; Wed, 4 Oct 2017 17:50:47 +1100 From: Anju T Sudhakar To: mpe@ellerman.id.au Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, maddy@linux.vnet.ibm.com, hemant@linux.vnet.ibm.com, anju@linux.vnet.ibm.com Subject: [PATCH] powerpc/perf: Fix for core/nest imc call trace on cpuhotplug Date: Wed, 4 Oct 2017 12:20:52 +0530 Message-Id: <1507099852-28004-1-git-send-email-anju@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Nest/core pmu units are enabled only when it is used. A reference count is maintained for the events which uses the nest/core pmu units. Currently in *_imc_counters_release function a WARN() is used for notification of any underflow of ref count. The case where event ref count hit a negative value is, when perf session is started, followed by offlining of all cpus in a given core. i.e. in cpuhotplug offline path ppc_core_imc_cpu_offline() function set the ref->count to zero, if the current cpu which is about to offline is the last cpu in a given core and make an OPAL call to disable the engine in that core. And on perf session termination, perf->destroy (core_imc_counters_release) will first decrement the ref->count for this core and based on the ref->count value an opal call is made to disable the core-imc engine. Now, since cpuhotplug path already clears the ref->count for core and disabled the engine, perf->destroy() decrementing again at event termination make it negative which in turn fires the WARN_ON. The same happens for nest units. Add a check to see if the reference count is alreday zero, before decrementing the count, so that the ref count will not hit a negative value. Signed-off-by: Anju T Sudhakar --- arch/powerpc/perf/imc-pmu.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c index 9ccac86f3463..e3a1f65933b5 100644 --- a/arch/powerpc/perf/imc-pmu.c +++ b/arch/powerpc/perf/imc-pmu.c @@ -399,6 +399,20 @@ static void nest_imc_counters_release(struct perf_event *event) /* Take the mutex lock for this node and then decrement the reference count */ mutex_lock(&ref->lock); + if (ref->refc == 0) { + /* + * The scenario where this is true is, when perf session is + * started, followed by offlining of all cpus in a given node. + * + * In the cpuhotplug offline path, ppc_nest_imc_cpu_offline() + * function set the ref->count to zero, if the cpu which is + * about to offline is the last cpu in a given node and make + * an OPAL call to disable the engine in that node. + * + */ + mutex_unlock(&ref->lock); + return; + } ref->refc--; if (ref->refc == 0) { rc = opal_imc_counters_stop(OPAL_IMC_COUNTERS_NEST, @@ -646,6 +660,20 @@ static void core_imc_counters_release(struct perf_event *event) return; mutex_lock(&ref->lock); + if (ref->refc == 0) { + /* + * The scenario where this is true is, when perf session is + * started, followed by offlining of all cpus in a given core. + * + * In the cpuhotplug offline path, ppc_core_imc_cpu_offline() + * function set the ref->count to zero, if the cpu which is + * about to offline is the last cpu in a given core and make + * an OPAL call to disable the engine in that core. + * + */ + mutex_unlock(&ref->lock); + return; + } ref->refc--; if (ref->refc == 0) { rc = opal_imc_counters_stop(OPAL_IMC_COUNTERS_CORE, -- 2.14.1