workqueue: Don't bind the rescuer in the last working cpu

So that when the rescuer is woken up next time, it will not interrupt
the last working cpu which might be busy on other crucial works but
have nothing to do with the rescuer's incoming works.

Cc: Valentin Schneider <[email protected]>
Signed-off-by: Lai Jiangshan <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>

Author: Lai Jiangshan

kernel/workqueue.c

@@ -2684,6 +2684,17 @@ static void worker_attach_to_pool(struct worker *worker,
 	mutex_unlock(&wq_pool_attach_mutex);
 }
 
+static void unbind_worker(struct worker *worker)
+{
+	lockdep_assert_held(&wq_pool_attach_mutex);
+
+	kthread_set_per_cpu(worker->task, -1);
+	if (cpumask_intersects(wq_unbound_cpumask, cpu_active_mask))
+		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask) < 0);
+	else
+		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
+}
+
 /**
  * worker_detach_from_pool() - detach a worker from its pool
  * @worker: worker which is attached to its pool
@@ -2701,7 +2712,7 @@ static void worker_detach_from_pool(struct worker *worker)
 
 	mutex_lock(&wq_pool_attach_mutex);
 
-	kthread_set_per_cpu(worker->task, -1);
+	unbind_worker(worker);
 	list_del(&worker->node);
 	worker->pool = NULL;
 
@@ -2796,17 +2807,6 @@ static struct worker *create_worker(struct worker_pool *pool)
 	return NULL;
 }
 
-static void unbind_worker(struct worker *worker)
-{
-	lockdep_assert_held(&wq_pool_attach_mutex);
-
-	kthread_set_per_cpu(worker->task, -1);
-	if (cpumask_intersects(wq_unbound_cpumask, cpu_active_mask))
-		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask) < 0);
-	else
-		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
-}
-
 static void wake_dying_workers(struct list_head *cull_list)
 {
 	struct worker *worker;