Possible LMB hot unplug bug in 4.13+ kernels

[Michael Ellerman]

Nathan Fontenot <nfont at linux.vnet.ibm.com> writes:
> On 10/04/2017 03:21 PM, Daniel Henrique Barboza wrote:
...
>> It appears that the hot unplug is failing because lmb_is_removable(lmb) is returning
>> false inside dlpar_remove_lmb, triggering the hotplug of the LMBs again:
...
>> 
>> I am not aware of anything that I can do from QEMU side to fix this. Can anyone take a look or provide
>> guidance? Am I missing something in my tests?
>> 
>
> I don't think you are missing anything in your tests and am not sure that this is a bug.
> DLPAR memory remove operations are not guaranteed, memory remove requests fail quite often
> because the LMBs we are trying to remove are not removable.
>
> From the added printks you put in this appears to be what is happening. When trying to
> remove the range of LMBs, one of the memory sections in one of the LMBs is not removbable,
> this is seen when lmb_is_removable() returns false.

Yeah I agree.

Unless you (Daniel) think there's some reason lmb_is_removable() is
incorrectly returning false. But most likely it's correct and there's
just an unmovable allocation in that range.

cheers