linux-kernel - Re: [PATCH] cpufreq: powernv: Check negative value returned by cpufreq_table_find_index

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Message-ID: <20180212102900.GU28462@vireshk-i7>
Date:   Mon, 12 Feb 2018 15:59:00 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
Cc:     rjw@...ysocki.net, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        mpe@...erman.id.au
Subject: Re: [PATCH] cpufreq: powernv: Check  negative value returned by
 cpufreq_table_find_index_dl()

On 12-02-18, 15:51, Shilpasri G Bhat wrote:
> This patch fixes the below Coverity warning:
> 
> *** CID 182816:  Memory - illegal accesses  (NEGATIVE_RETURNS)
> /drivers/cpufreq/powernv-cpufreq.c: 1008 in powernv_fast_switch()
> 1002     					unsigned int target_freq)
> 1003     {
> 1004     	int index;
> 1005     	struct powernv_smp_call_data freq_data;
> 1006
> 1007     	index = cpufreq_table_find_index_dl(policy, target_freq);
> >>>     CID 182816:  Memory - illegal accesses  (NEGATIVE_RETURNS)
> >>>     Using variable "index" as an index to array "powernv_freqs".
> 1008     	freq_data.pstate_id = powernv_freqs[index].driver_data;
> 1009     	freq_data.gpstate_id = powernv_freqs[index].driver_data;
> 1010     	set_pstate(&freq_data);
> 1011
> 1012     	return powernv_freqs[index].frequency;
> 1013     }
> 
> Signed-off-by: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
> ---
>  drivers/cpufreq/powernv-cpufreq.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
> index 29cdec1..69edfe9 100644
> --- a/drivers/cpufreq/powernv-cpufreq.c
> +++ b/drivers/cpufreq/powernv-cpufreq.c
> @@ -1005,6 +1005,9 @@ static unsigned int powernv_fast_switch(struct cpufreq_policy *policy,
>  	struct powernv_smp_call_data freq_data;
>  
>  	index = cpufreq_table_find_index_dl(policy, target_freq);
> +	if (unlikely(index < 0))
> +		index = get_nominal_index();
> +

AFAICT, you will get -1 here only if the freq table had no valid
frequencies (or the freq table is empty). Why would that happen ?

>  	freq_data.pstate_id = powernv_freqs[index].driver_data;
>  	freq_data.gpstate_id = powernv_freqs[index].driver_data;
>  	set_pstate(&freq_data);
> -- 
> 1.8.3.1

-- 
viresh