From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 87BBE19C553; Tue, 15 Apr 2025 08:50:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744707026; cv=none; b=bh5hQIT7fJSfgpgF2RUqEmuliGkLMTI6QA3azQ12ImMgxJemmDDc3kcThvWbNO3iT2vIqXBropVmDluyZNKpSKlWZwDFy785lYF07n+/9YiLJ8q2WmqIhQD6mvuYlMzBZrXQUTAmM1uUC/kV+Jpj/D7iDt83Atw4LhPAjbmKAEc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744707026; c=relaxed/simple; bh=n03h9Zy7GpkRKI6xjpJWJQOJLZGcig0IBGto/J35gn4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Nde0l6uBAb6zE8QXDG2XOV8/Hx2JogFeG7YpHwKhw8lC5UlrkxF2NQykdNyFRQ9ioZodz/a52ISotGwL1ssd5GcxiE09jHR+V2l7y2AuVWc2AkUXsDflFrFixtJAsrVKKojbjbBpmqamQUiTJ28ELOMaCmJzeITZY5Nup3l+qFI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3C6BE339; Tue, 15 Apr 2025 01:50:19 -0700 (PDT) Received: from [10.57.68.100] (unknown [10.57.68.100]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DA43A3F694; Tue, 15 Apr 2025 01:50:19 -0700 (PDT) Message-ID: <0fc11aa1-e329-4f0d-a547-1ead73111088@arm.com> Date: Tue, 15 Apr 2025 09:50:17 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] PM: EM: Fix potential division-by-zero error in em_compute_costs() To: Yaxiong Tian Cc: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, Yaxiong Tian , rafael@kernel.org References: Content-Language: en-US From: Lukasz Luba In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/14/25 10:04, Yaxiong Tian wrote: > From: Yaxiong Tian > > When the device is of a non-CPU type, table[i].performance won't be > initialized in the previous em_init_performance(), resulting in division > by zero when calculating costs in em_compute_costs(). > > Since the 'cost' algorithm is only used for EAS energy efficiency > calculations and is currently not utilized by other device drivers, we > should add the _is_cpu_device(dev) check to prevent this division-by-zero > issue. > > Fixes: <1b600da51073> ("PM: EM: Optimize em_cpu_energy() and remove division") > Signed-off-by: Yaxiong Tian > --- > kernel/power/energy_model.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c > index d9b7e2b38c7a..fc972cc1fc12 100644 > --- a/kernel/power/energy_model.c > +++ b/kernel/power/energy_model.c > @@ -235,7 +235,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table, > > /* Compute the cost of each performance state. */ > for (i = nr_states - 1; i >= 0; i--) { > - unsigned long power_res, cost; > + unsigned long power_res, cost = 0; > > if ((flags & EM_PERF_DOMAIN_ARTIFICIAL) && cb->get_cost) { > ret = cb->get_cost(dev, table[i].frequency, &cost); > @@ -244,7 +244,7 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table, > cost, ret); > return -EINVAL; > } > - } else { > + } else if (_is_cpu_device(dev)) { > /* increase resolution of 'cost' precision */ > power_res = table[i].power * 10; > cost = power_res / table[i].performance; LGTM, Reviewed-by: Lukasz Luba