[tip:perf/core] perf: Fix errors path in perf_output_begin()

From: tip-bot for Stephane Eranian
Date: Tue May 18 2010 - 13:17:56 EST

Commit-ID: 00d1d0b095ba4e5c0958cb228b2a9c445d4a339d
Gitweb: http://git.kernel.org/tip/00d1d0b095ba4e5c0958cb228b2a9c445d4a339d
Author: Stephane Eranian <eranian@xxxxxxxxxx>
AuthorDate: Mon, 17 May 2010 12:46:01 +0200
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Tue, 18 May 2010 18:35:47 +0200

perf: Fix errors path in perf_output_begin()

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

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

Signed-off-by: Stephane Eranian <eranian@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
LKML-Reference: <4bf13674.014fd80a.6c82.ffffb20c@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
kernel/perf_event.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 17ac47f..8d61d29 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3036,7 +3036,7 @@ 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)
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