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

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Message-Id: <14e2fe70-7628-4377-664d-3c4b0071e08d@linux.vnet.ibm.com>
Date:   Mon, 12 Feb 2018 16:03:42 +0530
From:   Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
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()

Hi,

On 02/12/2018 03:59 PM, Viresh Kumar wrote:
> 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 ?

I agree too. There is no way we can get -1 with initialized cpu frequency table.
We don't initialize powernv-cpufreq if we don't have valid CPU frequency
entries. Is there any other way to suppress the Coverity tool warning apart from
ignoring it?

Thanks and Regards,
Shilpa

> 
>>  	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
>