linux-kernel - Re: [PATCH v8 8/8] cpufreq: intel_pstate: Use CPPC to get max performance

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Date:   Wed, 07 Dec 2016 15:12:53 -0800
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     rjw@...ysocki.net, tglx@...utronix.de, mingo@...hat.com,
        bp@...e.de, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        x86@...nel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        peterz@...radead.org, jolsa@...hat.com,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v8 8/8] cpufreq: intel_pstate: Use CPPC to get max
 performance

On Wed, 2016-12-07 at 20:06 +0100, Sebastian Andrzej Siewior wrote:
> 
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  drivers/acpi/cppc_acpi.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index d0d0504b7c89..93252e5374c5 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -803,6 +803,7 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
>  		if (addr)
>  			iounmap(addr);
>  	}
> +	per_cpu(cpc_desc_ptr, pr->id) = NULL;
>  	kfree(cpc_ptr);
>  
>  out_buf_free:
> @@ -824,6 +825,8 @@ void acpi_cppc_processor_exit(struct acpi_processor *pr)
>  	void __iomem *addr;
>  
>  	cpc_ptr = per_cpu(cpc_desc_ptr, pr->id);
> +	if (!cpc_ptr)
> +		return;

I agree that not handling null pointer here is a bug that should be fixed.
The cpc_ptr is checked at other places like acpi_get_psd_map.  
We could potentially have a null cpc_ptr say when
the parsing of CPC table failed. We should handle such cases gracefully.

Tim