[PATCH 2/2] workqueue:Fix affinity of an unbound worker of a node with 1 online CPU

[Michael Ellerman]

Tejun Heo <htejun at gmail.com> writes:

> On Thu, Jun 16, 2016 at 02:45:48PM +0200, Peter Zijlstra wrote:
>> Subject: workqueue: Fix setting affinity of unbound worker threads
>> From: Peter Zijlstra <peterz at infradead.org>
>> Date: Thu Jun 16 14:38:42 CEST 2016
>> 
>> With commit e9d867a67fd03ccc ("sched: Allow per-cpu kernel threads to
>> run on online && !active"), __set_cpus_allowed_ptr() expects that only
>> strict per-cpu kernel threads can have affinity to an online CPU which
>> is not yet active.
>> 
>> This assumption is currently broken in the CPU_ONLINE notification
>> handler for the workqueues where restore_unbound_workers_cpumask()
>> calls set_cpus_allowed_ptr() when the first cpu in the unbound
>> worker's pool->attr->cpumask comes online. Since
>> set_cpus_allowed_ptr() is called with pool->attr->cpumask in which
>> only one CPU is online which is not yet active, we get the following
>> WARN_ON during an CPU online operation.
>
> Applied to wq/for-4.7-fixes.

It looks like this still hasn't gone to Linus for 4.7?

Could it please, it's a pretty nasty regression on our boxes.

cheers