[PATCH 3/6] perf_counter: sanity check on the output API

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

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Ensure we never write more than we said we would.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 kernel/perf_counter.c |    4 ++++
 1 file changed, 4 insertions(+)

Index: linux-2.6/kernel/perf_counter.c
===================================================================
--- linux-2.6.orig/kernel/perf_counter.c
+++ linux-2.6/kernel/perf_counter.c
@@ -1422,6 +1422,7 @@ struct perf_output_handle {
 	struct perf_counter *counter;
 	struct perf_mmap_data *data;
 	unsigned int offset;
+	unsigned int head;
 	int wakeup;
 };
 
@@ -1447,6 +1448,7 @@ static int perf_output_begin(struct perf
 	handle->counter = counter;
 	handle->data = data;
 	handle->offset = offset;
+	handle->head = head;
 	handle->wakeup = (offset >> PAGE_SHIFT) != (head >> PAGE_SHIFT);
 
 	return 0;
@@ -1478,6 +1480,8 @@ static void perf_output_copy(struct perf
 	} while (len);
 
 	handle->offset = offset;
+
+	WARN_ON(handle->offset > handle->head);
 }
 
 #define perf_output_put(handle, x) \

--