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() is perf_output_unlock().
This patch fixes the problem by adding a new label and skipping
perf_task_unlock() in case data->nr_pages is 0.
Signed-off-by: Stephane Eranian <eran...@google.com>
--
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index a4fa381..95137b6 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3035,8 +3035,10 @@ int perf_output_begin(struct perf_output_handle *handle,
handle->nmi = nmi;
handle->sample = sample;
- if (!data->nr_pages)
- goto fail;
+ if (!data->nr_pages) {
+ atomic_inc(&data->lost);
+ goto out;
+ }
have_lost = atomic_read(&data->lost);
if (have_lost)
------------------------------------------------------------------------------
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