From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753995AbcKASxb (ORCPT ); Tue, 1 Nov 2016 14:53:31 -0400 Received: from mail-yw0-f172.google.com ([209.85.161.172]:36106 "EHLO mail-yw0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751152AbcKASx3 (ORCPT ); Tue, 1 Nov 2016 14:53:29 -0400 From: David Carrillo-Cisneros To: linux-kernel@vger.kernel.org Cc: "x86@kernel.org" , Ingo Molnar , Thomas Gleixner , Andi Kleen , Kan Liang , Nilay Vaish , Peter Zijlstra , Vegard Nossum , Paul Turner , Stephane Eranian , David Carrillo-Cisneros Subject: [PATCH v2] perf/core: do not set cpuctx->cgrp for unscheduled cgroups Date: Tue, 1 Nov 2016 11:52:58 -0700 Message-Id: <1478026378-86083-1-git-send-email-davidcc@google.com> X-Mailer: git-send-email 2.8.0.rc3.226.g39d4020 In-Reply-To: <1476228453-63474-1-git-send-email-davidcc@google.com> References: <1476228453-63474-1-git-send-email-davidcc@google.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (v2 only extends this changelog.) commit db4a835601b7 ("perf/core: Set cgroup in CPU contexts for new cgroup events") failed to verify that event->cgrp is actually the scheduled cgroup in a CPU before setting cpuctx->cgrp. This patch fixes that. Now that there is a different path for scheduled and unscheduled cgroup, add a warning to catch when cpuctx->cgrp is still set after the last cgroup event has been unsheduled. To verify the bug: # Create 2 cgroups. mkdir /dev/cgroups/devices/g1 mkdir /dev/cgroups/devices/g2 # launch a task, bind it to a cpu and move it to g1 CPU=2 while :; do : ; done & P=$! taskset -pc $CPU $P echo $P > /dev/cgroups/devices/g1/tasks # monitor g2 (it runs no tasks) and observe output perf stat -e cycles -I 1000 -C $CPU -G g2 # time counts unit events 1.000091408 7,579,527 cycles g2 2.000350111 cycles g2 3.000589181 cycles g2 4.000771428 cycles g2 # note first line that displays that a task run in g2, despite # g2 having no tasks. This is because cpuctx->cgrp was wrongly # set when context of new event was installed. # After applying the fix we obtain the right output: perf stat -e cycles -I 1000 -C $CPU -G g2 # time counts unit events 1.000119615 cycles g2 2.000389430 cycles g2 3.000590962 cycles g2 Signed-off-by: David Carrillo-Cisneros --- kernel/events/core.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/kernel/events/core.c b/kernel/events/core.c index c6e47e9..55953db 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -902,6 +902,17 @@ list_update_cgroup_event(struct perf_event *event, * this will always be called from the right CPU. */ cpuctx = __get_cpu_context(ctx); + + /* Only set/clear cpuctx->cgrp if current task uses event->cgrp. */ + if (perf_cgroup_from_task(current, ctx) != event->cgrp) { + /* + * We are removing the last cpu event in this context. + * If that event is not active in this cpu, cpuctx->cgrp + * should've been cleared by perf_cgroup_switch. + */ + WARN_ON_ONCE(!add && cpuctx->cgrp); + return; + } cpuctx->cgrp = add ? event->cgrp : NULL; } -- 2.8.0.rc3.226.g39d4020