Re: [PATCH v3 5/5] thermal: cpu_cooling: update the cpu device when cpufreq updates the policy cpu

[Kapileshwar Singh]

On 03/03/15 13:07, Viresh Kumar wrote:
> On 3 March 2015 at 17:11, Kapileshwar Singh <kapileshwar.singh@xxxxxxx> wrote:
>> Yes I indeed tested the case where we cache the device pointer of the CPU for which the OPP's are populated.
>> When this CPU is hotplugged out, it invalidates the device pointer itself. Here are the error we get in dmesg:
> 
> What do you mean by 'invalidates the device pointer' ? that cpu_dev is NULL ?

The cpu_dev is not NULL but we get an erroneous OPP back. We found the problem lies in the way we calculate the frequency for the cluster.

>> <3>[67203.216774] opp_get_voltage: Invalid parameters
>> <3>[67203.326774] opp_get_voltage: Invalid parameters
>> <3>[67203.326774] opp_get_voltage: Invalid parameters
> 
> Have you handwritten them ? Why don't they precede with dev_pm_* ??

I have not handwritten them, It was from a Linaro 3.10 based kernel when I first noticed this issue but the same problem exists in mainline. 

Apologies for this I sent you an older trace which I had saved when I found the bug. Here is the trace I get from mainline

[ 5680.135339] dev_pm_opp_get_voltage: Invalid parameters
[ 5680.245528] dev_pm_opp_get_voltage: Invalid parameters
[ 5680.355432] dev_pm_opp_get_voltage: Invalid parameters
[ 5680.465521] dev_pm_opp_get_voltage: Invalid parameters
[ 5680.575599] dev_pm_opp_get_voltage: Invalid parameters
[ 5680.685817] dev_pm_opp_get_voltage: Invalid parameters
[ 5680.795556] dev_pm_opp_get_voltage: Invalid parameters
[ 5680.905598] dev_pm_opp_get_voltage: Invalid parameters

> 
>>
>> Which happens because:
>>
>> unsigned long dev_pm_opp_get_voltage(struct dev_pm_opp *opp)
>> {
>> ..
>>         tmp_opp = rcu_dereference(opp);
>>         if (unlikely(IS_ERR_OR_NULL(tmp_opp)) || !tmp_opp->available)
>>                 pr_err("%s: Invalid parameters\n", __func__);
> 
> This %s should print routine name ..
> 
>>         else
>> ..
>>
>> Which happens when
>>
>>         opp = dev_pm_opp_find_freq_exact(cpufreq_device->cpu_dev, freq_hz,
>>                                          true);
>>
>> returns a an erroneous or NULL OPP or the opp is unavailable (in the above condition)
> 

Update: This returns an erroneous  OPP

> Please goto the depth of this thing, as I don't think it should happen.
> 
> Over that I was asking you if you have tested the solution Javi gave,
> because OPPs
> wouldn't have been initialized for other CPUs once policy->cpu goes down.
I did test this but we were working with the assumption that OPPs should be populated for all the CPUs and also that OPPs are lost for a hotplugged CPU which I see is not the case. 

We have looked at this more closely and found that problem lies in:

	freq = cpufreq_quick_get(cpumask_any(&cpufreq_device->allowed_cpus));

which returns a NULL frequency as we are not checking for online CPUs here. We shall come up with a fix for this. Many thanks for helping us with the investigation.

Regards, 
KP

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