workqueue: Always queue work items to the newest PWQ for order workqueues

To ensure non-reentrancy, __queue_work() attempts to enqueue a work
item to the pool of the currently executing worker. This is not only
unnecessary for an ordered workqueue, where order inherently suggests
non-reentrancy, but it could also disrupt the sequence if the item is
not enqueued on the newest PWQ.

Just queue it to the newest PWQ and let order management guarantees
non-reentrancy.

Signed-off-by: Lai Jiangshan <[email protected]>
Fixes: 4c065db ("workqueue: Enable unbound cpumask update on ordered workqueues")
Cc: [email protected] # v6.9+
Signed-off-by: Tejun Heo <[email protected]>
(cherry picked from commit 74347be3edfd11277799242766edf844c43dd5d3)

Author: Lai Jiangshan

kernel/workqueue.c

@@ -2274,9 +2274,13 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
 	 * If @work was previously on a different pool, it might still be
 	 * running there, in which case the work needs to be queued on that
 	 * pool to guarantee non-reentrancy.
+	 *
+	 * For ordered workqueue, work items must be queued on the newest pwq
+	 * for accurate order management.  Guaranteed order also guarantees
+	 * non-reentrancy.  See the comments above unplug_oldest_pwq().
 	 */
 	last_pool = get_work_pool(work);
-	if (last_pool && last_pool != pool) {
+	if (last_pool && last_pool != pool && !(wq->flags & __WQ_ORDERED)) {
 		struct worker *worker;
 
 		raw_spin_lock(&last_pool->lock);