workqueue: clear POOL_DISASSOCIATED in rebind_workers()

The commit a9ab775b ("workqueue: directly restore CPU affinity of
workers from CPU_ONLINE") moved the pool->lock into rebind_workers()
without also moving "pool->flags &= ~POOL_DISASSOCIATED".

There is nothing wrong with "pool->flags &= ~POOL_DISASSOCIATED" not
being moved together, but there isn't any benefit either. We move it
into rebind_workers() and achieve these benefits:

1) Better readability.  POOL_DISASSOCIATED is cleared in
   rebind_workers() as expected.

2) When POOL_DISASSOCIATED is cleared, we can ensure that all the
   running workers of the pool are on the local CPU (pool->cpu).

tj: Cosmetic updates to the code and description.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -4542,6 +4542,7 @@ static void rebind_workers(struct worker_pool *pool)
 						  pool->attrs->cpumask) < 0);
 
 	spin_lock_irq(&pool->lock);
+	pool->flags &= ~POOL_DISASSOCIATED;
 
 	for_each_pool_worker(worker, pool) {
 		unsigned int worker_flags = worker->flags;
@@ -4643,15 +4644,10 @@ static int workqueue_cpu_up_callback(struct notifier_block *nfb,
 		for_each_pool(pool, pi) {
 			mutex_lock(&pool->attach_mutex);
 
-			if (pool->cpu == cpu) {
-				spin_lock_irq(&pool->lock);
-				pool->flags &= ~POOL_DISASSOCIATED;
-				spin_unlock_irq(&pool->lock);
-
+			if (pool->cpu == cpu)
 				rebind_workers(pool);
-			} else if (pool->cpu < 0) {
+			else if (pool->cpu < 0)
 				restore_unbound_workers_cpumask(pool, cpu);
-			}
 
 			mutex_unlock(&pool->attach_mutex);
 		}