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

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Message-ID: <8fea501c-b950-17bd-c710-c923b9af6e62@huawei.com>
Date:   Wed, 16 Aug 2023 15:27:21 +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

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.

I hope this makes sense, thanks.

-- 
BR
Liao, Chang