linux-kernel - Re: [PATCH] cpufreq: cppc: Add missing error pointer check

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Date:   Wed, 16 Aug 2023 16:22:19 +0800
From:   "Liao, Chang" <liaochang1@...wei.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
CC:     <rafael@...nel.org>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: cppc: Add missing error pointer check



在 2023/8/16 16:17, Viresh Kumar 写道:
> On 16-08-23, 15:27, Liao, Chang wrote:
>> Hi Viresh,
>>
>> 在 2023/8/16 11:46, Viresh Kumar 写道:
>>> On 16-08-23, 03:05, Liao Chang wrote:
>>>> The function cppc_freq_invariance_init() may failed to create
>>>> kworker_fie, make it more robust by checking the return value to prevent
>>>> an invalid pointer dereference in kthread_destroy_worker(), which called
>>>> from cppc_freq_invariance_exit().
>>>>
>>>> Signed-off-by: Liao Chang <liaochang1@...wei.com>
>>>> ---
>>>>  drivers/cpufreq/cppc_cpufreq.c | 21 ++++++++++++++-------
>>>>  1 file changed, 14 insertions(+), 7 deletions(-)
>>>
>>> I think why it was designed this way was to make the driver work,
>>> without invariance support, in the worst case instead of just failing
>>> completely. The invariance thing is a good to have feature, but not
>>> really necessary and so failing probing the driver for that isn't
>>> worth it. We should print all error messages though.
>>>
>> Thanks for pointing that out. I think you are right that the kworker created
>> in the cppc driver is not the only arch_freq_scale updater, the ARCH provided
>> updater has more priority than the driver, so the driver should still work even
>> without kworker_fie supports.
>>
>> If that is the case, i think the best thing to do is checking the error pointer
>> and printing an error message before calling kthread_destroy() in cppc_freq_invariance_exit(),
>> this is because at that point, it is really necessary to ensure the kworker_fie has
>> been initialized as expected, otherwise it will raise a NULL pointer exception.
> 
> Or just set fie_disabled to true ?
Yes, I agree.

> 
>> I hope this makes sense, thanks.
> 
> It does.
> 

-- 
BR
Liao, Chang