linux-kernel - [PATCH] perf tool cgroup: initialize cgroup refcnt with refcount

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Message-Id: <20170601200214.23859-1-davidcc@google.com>
Date:   Thu,  1 Jun 2017 13:02:14 -0700
From:   David Carrillo-Cisneros <davidcc@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        David Windsor <dwindsor@...il.com>, Tejun Heo <tj@...nel.org>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Stephane Eranian <eranian@...gle.com>,
        Paul Turner <pjt@...gle.com>,
        David Carrillo-Cisneros <davidcc@...gle.com>
Subject: [PATCH] perf tool cgroup: initialize cgroup refcnt with refcount_set

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                    /

Signed-off-by: David Carrillo-Cisneros <davidcc@...gle.com>
Change-Id: I8f00f61aaecce876e7df448bd7f850b20db13ef1
---
 tools/perf/util/cgroup.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/cgroup.c b/tools/perf/util/cgroup.c
index 03347748f3fa..7bbc19b3caf3 100644
--- a/tools/perf/util/cgroup.c
+++ b/tools/perf/util/cgroup.c
@@ -133,7 +133,10 @@ static int add_cgroup(struct perf_evlist *evlist, char *str)
 
 	return -1;
 found:
-	refcount_inc(&cgrp->refcnt);
+	if (refcount_read(&cgrp->refcnt) == 0)
+		refcount_set(&cgrp->refcnt, 1);
+	else
+		refcount_inc(&cgrp->refcnt);
 	counter->cgrp = cgrp;
 	return 0;
 }
-- 
2.13.0.219.gdb65acc882-goog