[PATCH 3/3] workqueue: Init rescuer's affinities as wq_unbound_cpumask

[Lai Jiangshan <jiangshanlai@gmail.com>]

From: Lai Jiangshan <jiangshan.ljs@antgroup.com>

The affinity to set to the rescuers should be consistent in all paths
when a rescuer is in detached state. The affinity could be either
wq_unbound_cpumask or unbound_effective_cpumask(wq).

Related paths:
       rescuer's worker_detach_from_pool()
       update wq_unbound_cpumask
       update wq's cpumask
       init_rescuer()

Both affinities are Ok as long as they are consistent in all paths.

In the commit 449b31ad2937 ("workqueue: Init rescuer's affinities as
the wq's effective cpumask") makes init_rescuer use
unbound_effective_cpumask(wq) which is consistent with then
apply_wqattrs_commit().

But using unbound_effective_cpumask(wq) requres much more code to
maintain the consistency, and it doesn't make much sense since the
affinity is only effective when the rescuer is not processing works.
wq_unbound_cpumask is more favorable.

So apply_wqattrs_commit() and the path of "updating wq's cpumask" had
been changed to not update the rescuer's affinity, and both the paths
of "updating wq_unbound_cpumask" and "rescuer's
worker_detach_from_pool()" had been changed to use wq_unbound_cpumask.

Now, make init_rescuer() use wq_unbound_cpumask for rescuer's affinity
and make all the paths consistent.

Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
---
 kernel/workqueue.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ccf03a0ff122..acec76a22ce4 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5644,10 +5644,13 @@ static int init_rescuer(struct workqueue_struct *wq)
 	}
 
 	wq->rescuer = rescuer;
-	if (wq->flags & WQ_UNBOUND)
-		kthread_bind_mask(rescuer->task, unbound_effective_cpumask(wq));
+
+	/* initial cpumask is consistent with the detached rescuer and unbind_worker() */
+	if (cpumask_intersects(wq_unbound_cpumask, cpu_active_mask))
+		kthread_bind_mask(rescuer->task, wq_unbound_cpumask);
 	else
 		kthread_bind_mask(rescuer->task, cpu_possible_mask);
+
 	wake_up_process(rescuer->task);
 
 	return 0;
-- 
2.19.1.6.gb485710b