[RFC PATCH 0/2 shit_A shit_B] workqueue: fix wq_numa bug

[Lai Jiangshan <laijs@cn.fujitsu.com>]

Hi, All

This patches are un-changloged, un-compiled, un-booted, un-tested,
they are just shits, I even hope them un-sent or blocked.

The patches include two -solutions-:

Shit_A:
  workqueue: reset pool->node and unhash the pool when the node is
    offline
  update wq_numa when cpu_present_mask changed

 kernel/workqueue.c | 107 +++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 84 insertions(+), 23 deletions(-)


Shit_B:
  workqueue: reset pool->node and unhash the pool when the node is
    offline
  workqueue: remove wq_numa_possible_cpumask
  workqueue: directly update attrs of pools when cpu hot[un]plug

 kernel/workqueue.c | 135 +++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 101 insertions(+), 34 deletions(-)


Both patch1 of the both solutions are: reset pool->node and unhash the pool,
it is suggested by TJ, I found it is a good leading-step for fixing the bug.

The other patches are handling wq_numa_possible_cpumask where the solutions
diverge.

Solution_A uses present_mask rather than possible_cpumask. It adds
wq_numa_notify_cpu_present_set/cleared() for notifications of
the changes of cpu_present_mask.  But the notifications are un-existed
right now, so I fake one (wq_numa_check_present_cpumask_changes())
to imitate them.  I hope the memory people add a real one.

Solution_B uses online_mask rather than possible_cpumask.
this solution remove more coupling between numa_code and workqueue,
it just depends on cpumask_of_node(node).

Patch2_of_Solution_B removes the wq_numa_possible_cpumask and add
overhead when cpu hot[un]plug, Patch3 reduce this overhead.

Thanks,
Lai


Reported-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: "Gu, Zheng" <guz.fnst@cn.fujitsu.com>
Cc: tangchen <tangchen@cn.fujitsu.com>
Cc: Hiroyuki KAMEZAWA <kamezawa.hiroyu@jp.fujitsu.com>
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