[PATCH -tip V4 4/8] workqueue: Manually break affinity on pool detachment

[Lai Jiangshan]

From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>

The pool->attrs->cpumask might be a single CPU and it may go
down after detachment, and the scheduler won't force to break
affinity for us since it is a per-cpu-ktrhead.  So we have to
do it on our own and unbind this worker which can't be unbound
by workqueue_offline_cpu() since it doesn't belong to any pool
after detachment.  Do it unconditionally for there is no harm
to break affinity for non-per-cpu-ktrhead and we don't need to
rely on the scheduler's policy on when to break affinity.

Fixes: 06249738a41a ("workqueue: Manually break affinity on hotplug")
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Tested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
---
 kernel/workqueue.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 3e92bc4f8a36..aed08eddeb83 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1888,6 +1888,19 @@ static void worker_detach_from_pool(struct worker *worker)
 
 	if (list_empty(&pool->workers))
 		detach_completion = pool->detach_completion;
+
+	/*
+	 * The pool->attrs->cpumask might be a single CPU and it may go
+	 * down after detachment, and the scheduler won't force to break
+	 * affinity for us since it is a per-cpu-ktrhead.  So we have to
+	 * do it on our own and unbind this worker which can't be unbound
+	 * by workqueue_offline_cpu() since it doesn't belong to any pool
+	 * after detachment.  Do it unconditionally for there is no harm
+	 * to break affinity for non-per-cpu-ktrhead and we don't need to
+	 * rely on the scheduler's policy on when to break affinity.
+	 */
+	set_cpus_allowed_ptr(worker->task, cpu_possible_mask);
+
 	mutex_unlock(&wq_pool_attach_mutex);
 
 	/* clear leftover flags without pool->lock after it is detached */
-- 
2.19.1.6.gb485710b