linux-kernel - Re: [PATCH -next] cpufreq: Fix reserved space in cpufreq_show

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Date:   Sat, 18 Jun 2022 18:32:16 +0800
From:   "yiyang (D)" <yiyang13@...wei.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
CC:     Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] cpufreq: Fix reserved space in cpufreq_show_cpus()


On 2022/6/15 12:56, Viresh Kumar wrote:
> On 14-06-22, 15:48, Rafael J. Wysocki wrote:
>> On Tue, Jun 14, 2022 at 3:37 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>>>
>>> On Tue, May 24, 2022 at 9:10 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>>>>
>>>> On 21-05-22, 14:35, Yi Yang wrote:
>>>>> Function scnprintf() would reserve space for the trailing '\0' and return
>>>>> value is the number of characters written into buf not including the
>>>>> trailing '\0'. internally meaning the next scnprintf() would write begin
>>>>> the trailing '\0'. The code specifying "PAGE_SIZE - i - 2" here is trying
>>>>> to reserve space for "\n\0" which would cause scnprintf() to reserve an
>>>>> additional byte making the tail of the buf looks like this: "\n\0\0".
>>>>> Thus. we should reserve only the space for one '\0'. passing in
>>>>> "PAGE_SIZE - i - 1".
>>>>>
>>>>> Additionally, each iteration would replace the trailing '\0' from the last
>>>>> iteration with a space, and append 4 additional bytes to the string making
>>>>> it a total of 5 additional bytes. That means we should stop printing into
>>>>> the buffer if the remaining size is less than 7 bytes(1 for the ' ', 4 for
>>>>> the %u and 2 for the tailing "\n\0")
>>>>>
>>>>> Signed-off-by: Yi Yang <yiyang13@...wei.com>
>>>>> ---
>>>>>   drivers/cpufreq/cpufreq.c | 6 +++---
>>>>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>>>>> index 1f6667ce43bd..60c005c9961e 100644
>>>>> --- a/drivers/cpufreq/cpufreq.c
>>>>> +++ b/drivers/cpufreq/cpufreq.c
>>>>> @@ -844,9 +844,9 @@ ssize_t cpufreq_show_cpus(const struct cpumask *mask, char *buf)
>>>>>
>>>>>        for_each_cpu(cpu, mask) {
>>>>>                if (i)
>>>>> -                     i += scnprintf(&buf[i], (PAGE_SIZE - i - 2), " ");
>>>>> -             i += scnprintf(&buf[i], (PAGE_SIZE - i - 2), "%u", cpu);
>>>>> -             if (i >= (PAGE_SIZE - 5))
>>>>> +                     i += scnprintf(&buf[i], (PAGE_SIZE - i - 1), " ");
>>>>> +             i += scnprintf(&buf[i], (PAGE_SIZE - i - 1), "%u", cpu);
>>>>> +             if (i >= (PAGE_SIZE - 6))
>>>>>                        break;
>>>>>        }
>>>>>        i += sprintf(&buf[i], "\n");
>>>>
>>>> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
>>>
>>> Applied as 5.20 material, thanks!
>>
>> And dropped, because it has been superseded by this one:
>>
>> https://patchwork.kernel.org/project/linux-pm/patch/b9fa08171c09343ace94a7343553a4bee4695c90.1653565641.git.viresh.kumar@linaro.org/
> 
> The $Subject patch is still required AFAICT, it is fixing a different problem.
> Though it needs to be rebased on top of your branch now.
> 

What can i do for this patch?

--
Yi