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From: Stephane Eranian on 17 May 2010 08:10
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 skipping perf_output_unlock()
in case data->nr_pages is 0 while maintaining the accounting
for data->lost.

Signed-off-by: Stephane Eranian <eranian(a)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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Prev: [ANNOUNCE] GSoC project: Improving kconfig using a SAT solver
Next: [PATCH] drivers/mfd: remove unneeded and dangerous clearing of clientdata