linux-kernel - Re: [PATCH] ftrace: Avoid potential division by zero in function_stat

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Message-Id: <20250205112154.1541872-1-kniv@yandex-team.ru>
Date: Wed,  5 Feb 2025 14:21:54 +0300
From: Nikolay Kuratov <kniv@...dex-team.ru>
To: linux-kernel@...r.kernel.org
Cc: linux-trace-kernel@...r.kernel.org,
	Wen Yang <wenyang@...ux.alibaba.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mark Rutland <mark.rutland@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	kniv@...dex-team.ru
Subject: Re: [PATCH] ftrace: Avoid potential division by zero in function_stat_show()

Oops, this still does not fix an overflow because of

> rec->time_square_sum += calltime * calltime;

We can't eliminate overflows easily without both using u64 and converting
ns to us prior to any squaring. I will send an appropriate patch later
if needed. Maybe we're a way too paranoid about overflows and really want
only not to divide by zero?