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

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Message-ID: <20230816081708.o36cvwi3wwh62cmu@vireshk-i7>
Date:   Wed, 16 Aug 2023 13:47:08 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Liao, Chang" <liaochang1@...wei.com>
Cc:     rafael@...nel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: cppc: Add missing error pointer check

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 ?

> I hope this makes sense, thanks.

It does.

-- 
viresh