workqueue: kick a worker in pwq_adjust_max_active()

If pwq_adjust_max_active() changes max_active from 0 to
saved_max_active, it needs to wakeup worker.  This is already done by
thaw_workqueues().

If pwq_adjust_max_active() increases max_active for an unbound wq,
while not strictly necessary for correctness, it's still desirable to
wake up a worker so that the requested concurrency level is reached
sooner.

Move wake_up_worker() call from thaw_workqueues() to
pwq_adjust_max_active() so that it can handle both of the above two
cases.  This also makes thaw_workqueues() simpler.

tj: Updated comments and description.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -3598,6 +3598,12 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq)
 		while (!list_empty(&pwq->delayed_works) &&
 		       pwq->nr_active < pwq->max_active)
 			pwq_activate_first_delayed(pwq);
+
+		/*
+		 * Need to kick a worker after thawed or an unbound wq's
+		 * max_active is bumped.  It's a slow path.  Do it always.
+		 */
+		wake_up_worker(pwq->pool);
 	} else {
 		pwq->max_active = 0;
 	}
@@ -4401,13 +4407,6 @@ void thaw_workqueues(void)
 	}
 	spin_unlock_irq(&pwq_lock);
 
-	/* kick workers */
-	for_each_pool(pool, pi) {
-		spin_lock_irq(&pool->lock);
-		wake_up_worker(pool);
-		spin_unlock_irq(&pool->lock);
-	}
-
 	workqueue_freezing = false;
 out_unlock:
 	mutex_unlock(&wq_mutex);