Re: Null pointer crash at find_idlest_group on db845c w/ linus/master

[Valentin Schneider]

On 04/12/2019 12:08, Vincent Guittot wrote:
>> Also; does it really have to involve an affinity "race"? AFAIU affinity
>> could have been changed a while back, but the waking CPU isn't allowed
>> so we skip the local_group (in simpler cases where each CPU is a group).
> 
> In fact, this will depend of the uninitialized values of local_sgs. I
> have been able to reproduce the situation where we skip local group
> but not to trigger the crash because the values already in the stack
> don't trigger the misfit comparison.
> 

One more thing, DB845 has a single DynamIQ cluster that is represented as a
flat hierarchy (unlike regular big.LITTLE, see
arch/arm64/boot/dts/qcom/sdm845.dtsi) so we'll just have a single MC level
with groups being individual CPUs, making the bug easier to reproduce
(than on regular big.LITTLE, that is). 

> I  wait for John feedback to confirm that this fix his problem and
> will send a clean version of the patch
>>
>>