On 03/03/15 13:07, Viresh Kumar wrote:
> On 3 March 2015 at 17:11, Kapileshwar Singh <[email protected]> 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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