[PATCH] perf_events: fix errors path in perf_output_begin() (take 3)

[Stephane Eranian]

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.

Signed-off-by: Stephane Eranian <eranian@xxxxxxxxxx>

--

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index a4fa381..4fdb919 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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