From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754698AbdGUQ5S (ORCPT ); Fri, 21 Jul 2017 12:57:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:58680 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753527AbdGUQzt (ORCPT ); Fri, 21 Jul 2017 12:55:49 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6759F21D3F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=acme@kernel.org Date: Fri, 21 Jul 2017 13:55:35 -0300 From: Arnaldo Carvalho de Melo To: David Carrillo-Cisneros Cc: linux-kernel@vger.kernel.org, Jiri Olsa , Kees Kook , Sudeep Holla , Alexander Shishkin , Wang Nan , Elena Reshetova , Stephane Eranian , Paul Turner Subject: Re: [PATCH 1/4] perf tool cgroup: Initialize cgroup refcnt with refcount_set Message-ID: <20170721165535.GK4134@kernel.org> References: <20170719011839.99399-1-davidcc@google.com> <20170719011839.99399-2-davidcc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170719011839.99399-2-davidcc@google.com> X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.8.3 (2017-05-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Tue, Jul 18, 2017 at 06:18:36PM -0700, David Carrillo-Cisneros escreveu: > Atomic reference counters were replaced by refcount_t in > commit 79c5fe6db8c7 ("perf/core: Fix error handling in perf_event_alloc()") > > In util/cgroup.c atomic_inc was replaced by refcount_inc, but the latter > is not mean to initiliaze refcounts with zero value. Add a path > to initialize cgrp->refcnt == 0 using refcount_set. > > Before this patch: > > $ perf stat -e cycles -C 0 -G / > perf_before: /usr/local/.../tools/include/linux/refcount.h:108: refcount_inc: Assertion `!(!refcount_inc_not_zero(r))' failed. > Aborted (core dumped) > > After this patch: > > $ perf stat -e cycles -C 0 -G / > Performance counter stats for 'CPU(s) 0': > 17,516,664 cycles / Ok, so this one was also reported by Brendan and I came up with an alternative patch, that follows the usual sequence of steps, see below. - Arnaldo commit b13ca9843c4ea07c5a1dbf0295986b5dfeb6ef6f Author: Arnaldo Carvalho de Melo Date: Tue Jul 18 20:20:19 2017 -0300 perf cgroup: Fix refcount usage When converting from atomic_t to refcount_t we didn't follow the usual step of initializing it to one before taking any new reference, which trips over checking if taking a reference for a freed refcount_t, fix it. Brendan's report: --- It's 4.12-rc7, with node v4.4.1. I'm building 4.13-rc1 now, as I hit what I think is another unrelated perf bug and I'm starting to wonder what else is broken on that version: (root) /mnt/src/linux-4.12-rc7/tools/perf # ./perf record -F 99 -a -e cpu-clock --cgroup=docker/f9e9d5df065b14646e8a11edc837a13877fd90c171137b2ba3feb67a0201cb65 -g perf: /mnt/src/linux-4.12-rc7/tools/include/linux/refcount.h:108: refcount_inc: Assertion `!(!refcount_inc_not_zero(r))' failed. Aborted that used to work... --- Testing it: Before: # perf stat -e cycles -C 0 --cgroup / perf: /home/acme/git/linux/tools/include/linux/refcount.h:108: refcount_inc: Assertion `!(!refcount_inc_not_zero(r))' failed. Aborted (core dumped) # After: # perf stat -e cycles -C 0 --cgroup / ^C Performance counter stats for 'CPU(s) 0': 132,081,393 cycles / 2.492942763 seconds time elapsed # Reported-by: Brendan Gregg Acked-by: Elena Reshetova Cc: Alexander Shishkin Cc: David Ahern Cc: David Carrillo-Cisneros Cc: Kees Kook Cc: Krister Johansen Cc: Paul Turner Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Sudeep Holla Cc: Thomas-Mich Richter Cc: Wang Nan Fixes: 79c5fe6db8c7 ("perf cgroup: Convert cgroup_sel.refcnt from atomic_t to refcount_t") Link: http://lkml.kernel.org/n/tip-l7ovfblq14ip2i08m1g0fkhv@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo diff --git a/tools/perf/util/cgroup.c b/tools/perf/util/cgroup.c index 03347748f3fa..0e77bc9e5f3c 100644 --- a/tools/perf/util/cgroup.c +++ b/tools/perf/util/cgroup.c @@ -98,8 +98,10 @@ static int add_cgroup(struct perf_evlist *evlist, char *str) cgrp = counter->cgrp; if (!cgrp) continue; - if (!strcmp(cgrp->name, str)) + if (!strcmp(cgrp->name, str)) { + refcount_inc(&cgrp->refcnt); break; + } cgrp = NULL; } @@ -110,6 +112,7 @@ static int add_cgroup(struct perf_evlist *evlist, char *str) return -1; cgrp->name = str; + refcount_set(&cgrp->refcnt, 1); cgrp->fd = open_cgroup(str); if (cgrp->fd == -1) { @@ -128,12 +131,11 @@ static int add_cgroup(struct perf_evlist *evlist, char *str) goto found; n++; } - if (refcount_read(&cgrp->refcnt) == 0) + if (refcount_dec_and_test(&cgrp->refcnt)) free(cgrp); return -1; found: - refcount_inc(&cgrp->refcnt); counter->cgrp = cgrp; return 0; }