From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1EF96250C1A; Wed, 5 Mar 2025 18:01:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741197679; cv=none; b=OBh+5kdzgz00OqWNYEI0Mn02TE96teAwxOOOw+ejsniYgL7SFp2u7C3T8mZzsd9QvoLaq08z2rz63mcgF7ua0nPK1/YzKW2LKvJoYJDDdx1q2F6Jt80EAKVbY71pyN6eiOPj6bngkVbr3kodFK7TBjHZdXa43ZzD4GKteVQc/gw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741197679; c=relaxed/simple; bh=ZdSpyPsMk5TiEvzkbNIRHg2wzwy6ITuV96wVqPngvAk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=auK2trMsfS1uOPX4flbfjTIkzxXMfPPaoEMfjI9f31FVePQCbC/9lA6pHdrrl1/IvYIQxHsWcC6ZbqTJ6drxjPe9a6rOTO5kxjcd3L24ZLZsRUdCkxMB6QEGM0Hn/JmtJSq4f4XV4kaYVzaJDlZciwAL5jfw+bvDomb45o0BQD8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Y7/nURLH; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Y7/nURLH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9F36EC4CEE0; Wed, 5 Mar 2025 18:01:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1741197679; bh=ZdSpyPsMk5TiEvzkbNIRHg2wzwy6ITuV96wVqPngvAk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Y7/nURLHIWD61Pz63Nf+GWf4SyDAJwbeEQCP48fXNcJyYSdnX5ElcXack6eOUrjeH If3rzRVnUAL6ryeJqlMzIsx36KJBGjMmN+bcg9UL8KMt/RhyNywafGPuDsUHb0tBJo 1wpFGbGdgedefLmNmwm4MDZwymd1CXeDskxDjs5k= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Wen Yang , Mark Rutland , Mathieu Desnoyers , Nikolay Kuratov , "Steven Rostedt (Google)" Subject: [PATCH 6.6 062/142] ftrace: Avoid potential division by zero in function_stat_show() Date: Wed, 5 Mar 2025 18:48:01 +0100 Message-ID: <20250305174502.830142337@linuxfoundation.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250305174500.327985489@linuxfoundation.org> References: <20250305174500.327985489@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nikolay Kuratov commit a1a7eb89ca0b89dc1c326eeee2596f263291aca3 upstream. Check whether denominator expression x * (x - 1) * 1000 mod {2^32, 2^64} produce zero and skip stddev computation in that case. For now don't care about rec->counter * rec->counter overflow because rec->time * rec->time overflow will likely happen earlier. Cc: stable@vger.kernel.org Cc: Wen Yang Cc: Mark Rutland Cc: Mathieu Desnoyers Link: https://lore.kernel.org/20250206090156.1561783-1-kniv@yandex-team.ru Fixes: e31f7939c1c27 ("ftrace: Avoid potential division by zero in function profiler") Signed-off-by: Nikolay Kuratov Signed-off-by: Steven Rostedt (Google) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/ftrace.c | 27 ++++++++++++--------------- 1 file changed, 12 insertions(+), 15 deletions(-) --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -538,6 +538,7 @@ static int function_stat_show(struct seq static struct trace_seq s; unsigned long long avg; unsigned long long stddev; + unsigned long long stddev_denom; #endif mutex_lock(&ftrace_profile_lock); @@ -559,23 +560,19 @@ static int function_stat_show(struct seq #ifdef CONFIG_FUNCTION_GRAPH_TRACER seq_puts(m, " "); - /* Sample standard deviation (s^2) */ - if (rec->counter <= 1) - stddev = 0; - else { - /* - * Apply Welford's method: - * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2) - */ + /* + * 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);