From 873f3ba5d222ac2b0aa60ef0dc647fc9d9c0e7a3 Mon Sep 17 00:00:00 2001
From: Stephane Eranian <eranian@google.com>
Date: Mon, 17 May 2010 12:46:01 +0200
Subject: [PATCH] perf: Fix errors path in perf_output_begin()

commit ea2d2a0d32a1f98d5c1be461b715009ca7774156 in tip.

In case the sampling buffer has no "payload" pages,
nr_pages is 0. The problem is that the error path in
perf_output_begin() skips to a label which assumes
perf_output_lock() has been issued which is not the
case. That triggers a WARN_ON() in
perf_output_unlock().

This patch fixes the problem by skipping
perf_output_unlock() in case data->nr_pages is 0.

[ upstream commit: 00d1d0b095ba4e5c0958cb228b2a9c445d4a339d ]

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4bf13674.014fd80a.6c82.ffffb20c@mx.google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index ee1d0ab..395369a 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -2881,7 +2881,7 @@ int perf_output_begin(struct perf_output_handle *handle,
 	handle->sample	= sample;
 
 	if (!data->nr_pages)
-		goto fail;
+		goto out;
 
 	have_lost = atomic_read(&data->lost);
 	if (have_lost)
-- 
1.7.1.1