| From: Wen Yang <wenyang@linux.alibaba.com> |
| Date: Fri, 3 Jan 2020 11:02:48 +0800 |
| Subject: ftrace: Avoid potential division by zero in function profiler |
| |
| commit e31f7939c1c27faa5d0e3f14519eaf7c89e8a69d upstream. |
| |
| 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 |
| |
| 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> |
| [bwh: Backported to 3.16: adjust context] |
| Signed-off-by: Ben Hutchings <ben@decadent.org.uk> |
| --- |
| kernel/trace/ftrace.c | 6 +++--- |
| 1 file changed, 3 insertions(+), 3 deletions(-) |
| |
| --- a/kernel/trace/ftrace.c |
| +++ b/kernel/trace/ftrace.c |
| @@ -595,8 +595,7 @@ static int function_stat_show(struct seq |
| |
| #ifdef CONFIG_FUNCTION_GRAPH_TRACER |
| seq_printf(m, " "); |
| - avg = rec->time; |
| - do_div(avg, rec->counter); |
| + avg = div64_ul(rec->time, rec->counter); |
| |
| /* Sample standard deviation (s^2) */ |
| if (rec->counter <= 1) |
| @@ -613,7 +612,8 @@ static int function_stat_show(struct seq |
| * 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); |
