linux-kernel - Re: [PATCH v2 01/18] arm64: topology: Use __free(put_cpufreq

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Message-ID: <6f6c1e35-101d-4ef1-ac6e-5db337ccdd84@kylinos.cn>
Date: Thu, 28 Aug 2025 10:32:46 +0800
From: Zihuan Zhang <zhangzihuan@...inos.cn>
To: Sudeep Holla <sudeep.holla@....com>, Ben Horgan <ben.horgan@....com>
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Subject: Re: [PATCH v2 01/18] arm64: topology: Use __free(put_cpufreq_policy)
 for policy reference

在 2025/8/27 17:17, Sudeep Holla 写道:
> On Wed, Aug 27, 2025 at 09:30:13AM +0100, Ben Horgan wrote:
>> Hi Zihuan,
>>
>> On 8/27/25 03:31, Zihuan Zhang wrote:
>>> Replace the manual cpufreq_cpu_put() with __free(put_cpufreq_policy)
>>> annotation for policy references. This reduces the risk of reference
>>> counting mistakes and aligns the code with the latest kernel style.
>>>
>>> No functional change intended.
>>>
>>> Signed-off-by: Zihuan Zhang <zhangzihuan@...inos.cn>
>>> ---
>>>   arch/arm64/kernel/topology.c | 9 +++------
>>>   1 file changed, 3 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
>>> index 5d07ee85bdae..e3cb6d54f35b 100644
>>> --- a/arch/arm64/kernel/topology.c
>>> +++ b/arch/arm64/kernel/topology.c
>>> @@ -307,17 +307,16 @@ int arch_freq_get_on_cpu(int cpu)
>>>   		 */
>>>   		if (!housekeeping_cpu(cpu, HK_TYPE_TICK) ||
>>>   		    time_is_before_jiffies(last_update + msecs_to_jiffies(AMU_SAMPLE_EXP_MS))) {
>>> -			struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
>>> +			struct cpufreq_policy *policy __free(put_cpufreq_policy);
>> Based on the guidance, in include/linux/cleanup.h, I would expect the
>> assignment to be done on this line.
>>
>> "...the recommendation is to always define and assign variables in one
>>   * statement and not group variable definitions at the top of the
>>   * function when __free() is used."
>>
> Agreed. I did something similar recently and there was a code path where
> variable wasn't initialised and ended up with freeing unassigned pointer.
> So it is more than just a recommendation sometimes.
>
Thanks a lot for your suggestions.

We are also considering introducing a WITH_CPUFREQ_POLICY wrapper to 
encapsulate the cpufreq_cpu_get/put usage, so that the release order 
won’t be accidentally changed.

Link: 
https://lore.kernel.org/all/874d821e-8ea3-40ac-921b-c19bb380a456@kylinos.cn/

Do you have any suggestions or preferences on this direction?