ring-buffer: check for divide by zero in ring-buffer-benchmark

Although we check if "missed" is not zero, we divide by hit + missed,
and the addition can possible overflow and become a divide by zero.

This patch checks for this case, and will report it when it happens
then modify "hit" to make the calculation be non zero.

[ Impact: prevent possible divide by zero in ring-buffer-benchmark ]

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/kernel/trace/ring_buffer_benchmark.c b/kernel/trace/ring_buffer_benchmark.c
index 7d3aef93c49f..8d68e149a8b3 100644
--- a/kernel/trace/ring_buffer_benchmark.c
+++ b/kernel/trace/ring_buffer_benchmark.c
@@ -294,6 +294,12 @@ static void ring_buffer_producer(void)
 
                 pr_info("Total iterations per millisec: %ld\n", hit + missed);
 
+                /* it is possible that hit + missed will overflow and be zero */
+                if (!(hit + missed)) {
+                        pr_info("hit + missed overflowed and totalled zero!\n");
+                        hit--; /* make it non zero */
+                }
+
                 /* Caculate the average time in nanosecs */
                 avg = NSEC_PER_MSEC / (hit + missed);
                 pr_info("%ld ns per entry\n", avg);