[PATCH 6.18 22/83] workqueue: Add pool_workqueue to pending_pwqs list when unplugging multiple inactive works

[Greg Kroah-Hartman]

6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matthew Brost <matthew.brost@xxxxxxxxx>

commit 703ccb63ae9f7444d6ff876d024e17f628103c69 upstream.

In unplug_oldest_pwq(), the first inactive work item on the
pool_workqueue is activated correctly. However, if multiple inactive
works exist on the same pool_workqueue, subsequent works fail to
activate because wq_node_nr_active.pending_pwqs is empty — the list
insertion is skipped when the pool_workqueue is plugged.

Fix this by checking for additional inactive works in
unplug_oldest_pwq() and updating wq_node_nr_active.pending_pwqs
accordingly.

Fixes: 4c065dbce1e8 ("workqueue: Enable unbound cpumask update on ordered workqueues")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Carlos Santa <carlos.santa@xxxxxxxxx>
Cc: Ryan Neph <ryanneph@xxxxxxxxxx>
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Acked-by: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/workqueue.c |   14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1855,8 +1855,20 @@ static void unplug_oldest_pwq(struct wor
 	raw_spin_lock_irq(&pwq->pool->lock);
 	if (pwq->plugged) {
 		pwq->plugged = false;
-		if (pwq_activate_first_inactive(pwq, true))
+		if (pwq_activate_first_inactive(pwq, true)) {
+			/*
+			 * While plugged, queueing skips activation which
+			 * includes bumping the nr_active count and adding the
+			 * pwq to nna->pending_pwqs if the count can't be
+			 * obtained. We need to restore both for the pwq being
+			 * unplugged. The first call activates the first
+			 * inactive work item and the second, if there are more
+			 * inactive, puts the pwq on pending_pwqs.
+			 */
+			pwq_activate_first_inactive(pwq, false);
+
 			kick_pool(pwq->pool);
+		}
 	}
 	raw_spin_unlock_irq(&pwq->pool->lock);
 }