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ftrace: Avoid potential division by zero in function profiler

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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: e330b3bcd8 ("tracing: Show sample std dev in function profiling")
Fixes: 34886c8bc5 ("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>
This commit is contained in:
Wen Yang 2020-01-03 11:02:48 +08:00 committed by Steven Rostedt (VMware)
parent b8299d362d
commit e31f7939c1
1 changed files with 3 additions and 3 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

6
kernel/trace/ftrace.c
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@ -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);