On Mon, Aug 21, 2017 at 03:49:50PM +0200, Laurent Vivier wrote:

In wq_numa_init() a list of NUMA nodes with their list of possible CPUs
is built.

Unfortunately, on powerpc, the Firmware is only able to provide the
node of a CPU if the CPU is present. So, in our case (possible CPU)
CPU ids are known, but as the CPU is not present, the node id is
unknown and all the unplugged CPUs are attached to node 0.

This is something powerpc needs to fix.  Workqueue isn't the only one
making this assumption.  mm as a whole assumes that CPU <-> node
mapping is stable regardless of hotplug events.  Powerpc people know
about the issue and AFAIK are working on it.

Thanks.

-- 
tejun