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 897A7253339; Wed, 5 Mar 2025 18:09:22 +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=1741198162; cv=none; b=cm/AUaL/ow18+mPk2iiMRSQaZKSXPP29yFzTUnNzes1kDUTXDCtZM1qSFTEd6kWOflXek8iRLLOCPtt59UnIlhv8wrTbFA9wGE7nZDKV4yGn/JOHrmBjHNp4KoQrzqDLEj9ReDQTncNLZx3x3izlVaDEyEGta+nIduD9C/UY3Lk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741198162; c=relaxed/simple; bh=gh11XbluZkfCWfsTROrFjthVWBVouCOsXKXFJBKPEJQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GI/VuWKbEHhPD1/5Npd4dfA/Wifki5JJERMQlQdu2VdwepkHo2x70r3VSTiiVIKBv5nOV+TDFsc1jMFQpVlmpKXi0ygdHg2fu4eS3EXLjBscQ2Hp7vJC2ph/MlR7Mc6TUMApmqN69gP4dEFl/iqJ5xQ//YvVc5KHgPLqHqsdK48= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=IyFk3ol7; 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="IyFk3ol7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0B7B1C4CEE0; Wed, 5 Mar 2025 18:09:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1741198162; bh=gh11XbluZkfCWfsTROrFjthVWBVouCOsXKXFJBKPEJQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=IyFk3ol7diwFB5Hfpzu2lPqPc58FG0atrYmmLB9UrtHyjyN98FItWgGx+1Lm3C/gC nKOpeyNBff9DG6Q/4bw0E5d6uldjnG+wmzQ0d2YSSyOMI95AytmSGmF4eyZokzJD2a kGwC62FDsrgQpUIE2wIVUTiRIOlCnzKUaILiBmLw= 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 6.12 086/150] ftrace: Avoid potential division by zero in function_stat_show() Date: Wed, 5 Mar 2025 18:48:35 +0100 Message-ID: <20250305174507.269067942@linuxfoundation.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250305174503.801402104@linuxfoundation.org> References: <20250305174503.801402104@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 6.12-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 @@ -541,6 +541,7 @@ 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); @@ -562,23 +563,19 @@ 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);