Re: [PATCH] ftrace: Avoid potential division by zero in function_stat_show()

On Fri, 31 Jan 2025 18:53:46 +0300 Nikolay Kuratov kniv@yandex-team.ru wrote:

--- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -570,12 +570,12 @@ static int function_stat_show(struct seq_file *m, void *v) stddev = rec->counter * rec->time_squared - rec->time * rec->time;

• stddev = div64_ul(stddev, rec->counter * (rec->counter - 1));
  

  /*
  • Divide only 1000 for ns^2 -> us^2 conversion.
  • trace_print_graph_duration will divide 1000 again.
  */

• stddev = div64_ul(stddev,
  

• 		  rec->counter * (rec->counter - 1) * 1000);
  

• stddev = div64_ul(stddev, 1000);
  

  }

Why make it more complex than it needs to be? We can simply have:

if (rec->counter <= 1) { stddev = 0; } else { unsigned long counter = rec->counter * (rec->counter - 1) * 1000;

stddev = rec->counter * rec->time_squared - rec->time * rec->time;

/* Check for overflow */ stddev = counter > rec->counter ? div64_ul(stddev, counter) : 0; }

And be done with it.

I'll make the change and give you a "Reported-by".

Thanks,

-- Steve