ftrace: Avoid potential division by zero in function profiler

The ftrace_profile->counter is unsigned long and
do_div truncates it to 32 bits, which means it can test
non-zero and be truncated to zero for division.
Fix this issue by using div64_ul() instead.

Link: http://lkml.kernel.org/r/20200103030248.14516-1-wenyang@linux.alibaba.com
Cc: stable@vger.kernel.org
Fixes: e330b3bcd8319 ("tracing: Show sample std dev in function profiling")
Fixes: 34886c8bc590f ("tracing: add average time in function to function profiler")
Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index ac99a35..9bf1f2c 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -526,8 +526,7 @@ static int function_stat_show(struct seq_file *m, void *v)
        }
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-       avg = rec->time;
-       do_div(avg, rec->counter);
+       avg = div64_ul(rec->time, rec->counter);
        if (tracing_thresh && (avg < tracing_thresh))
                goto out;
 #endif
@@ -553,7 +552,8 @@ static int function_stat_show(struct seq_file *m, void *v)
                 * Divide only 1000 for ns^2 -> us^2 conversion.
                 * trace_print_graph_duration will divide 1000 again.
                 */
-               do_div(stddev, rec->counter * (rec->counter - 1) * 1000);
+               stddev = div64_ul(stddev,
+                                 rec->counter * (rec->counter - 1) * 1000);
        }
 
        trace_seq_init(&s);