linux-kernel - Re: [PATCH v2] PM: EM: Fix potential division-by-zero error in em_compute

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <tencent_C16C813B177E434BEAC73E842C46D872BC09@qq.com>
Date: Mon, 14 Apr 2025 17:08:44 +0800
From: Yaxiong Tian <iambestgod@...com>
To: Lukasz Luba <lukasz.luba@....com>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Yaxiong Tian <tianyaxiong@...inos.cn>, rafael@...nel.org
Subject: Re: [PATCH v2] PM: EM: Fix potential division-by-zero error in
 em_compute_costs()



在 2025/4/14 16:08, Lukasz Luba 写道:
> Hi Yaxiong,
> 
> On 4/11/25 02:28, Yaxiong Tian wrote:
>> From: Yaxiong Tian <tianyaxiong@...inos.cn>
>>
>> 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 <tianyaxiong@...inos.cn>
>> ---
>>   kernel/power/energy_model.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
>> index d9b7e2b38c7a..d1fa7e8787b5 100644
>> --- a/kernel/power/energy_model.c
>> +++ b/kernel/power/energy_model.c
>> @@ -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;
> 
> 
> As the test robot pointed out, please set the 'cost' to 0
> where it's declared.
> 
> The rest should be fine.
> 
> Regards,
> Lukasz

Okay.
I wasn’t sure whether the new patch should reuse the current Message-ID
or create a new one, so I checked with ChatGPT and kept the original
Message-ID for v2. If a new Message-ID is required, I can resend the
email.