Unverified Commit 74c40b7b authored by openeuler-ci-bot's avatar openeuler-ci-bot Committed by Gitee
Browse files

!15740 ftrace: Avoid potential division by zero in function_stat_show() 

Merge Pull Request from: @ci-robot 
 
PR sync from: Pu Lehui <pulehui@huawei.com>
https://mailweb.openeuler.org/archives/list/kernel@openeuler.org/message/226KCNU475WKUGRAL5RLAYKWALAJOGJA/ 
 
https://gitee.com/openeuler/kernel/issues/IBY5DV 
 
Link:https://gitee.com/openeuler/kernel/pulls/15740

 

Reviewed-by: default avatarYe Weihua <yeweihua4@huawei.com>
Reviewed-by: default avatarYuan Can <yuancan@huawei.com>
Signed-off-by: default avatarYuan Can <yuancan@huawei.com>
parents ee997750 e0a4f46c

kernel/trace/ftrace.c

+12 −15
Original line number Diff line number Diff line
@@ -544,6 +544,7 @@ static int function_stat_show(struct seq_file *m, void *v) 
	static struct trace_seq s;

	unsigned long long avg;

	unsigned long long stddev;

	unsigned long long stddev_denom;

#endif

	mutex_lock(&ftrace_profile_lock);
@@ -565,23 +566,19 @@ static int function_stat_show(struct seq_file *m, void *v) 
#ifdef CONFIG_FUNCTION_GRAPH_TRACER

	seq_puts(m, "    ");



	/* Sample standard deviation (s^2) */

	if (rec->counter <= 1)

		stddev = 0;

	else {

	/*

		 * Apply Welford's method:

	 * Variance formula:

	 * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2)

	 * Maybe Welford's method is better here?

	 * Divide only by 1000 for ns^2 -> us^2 conversion.

	 * trace_print_graph_duration will divide by 1000 again.

	 */

	stddev = 0;

	stddev_denom = rec->counter * (rec->counter - 1) * 1000;

	if (stddev_denom) {

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

			 rec->time * rec->time;



		/*

		 * 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, stddev_denom);

	}



	trace_seq_init(&s);