Merge tag 'wq-for-7.0-rc7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq

Pull workqueue fix from Tejun Heo:
 "This is a fix for a stall which triggers on ordered workqueues when
  there are multiple inactive work items during workqueue property
  changes through sysfs, which doesn't happen that frequently.

  While really late, the fix is very low risk as it just repeats an
  operation which is already being performed:

   - Fix incomplete activation of multiple inactive works when
     unplugging a pool_workqueue, where the pending_pwqs list
     wasn't being updated for subsequent works"

* tag 'wq-for-7.0-rc7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
  workqueue: Add pool_workqueue to pending_pwqs list when unplugging multiple inactive works

1 files changed, 13 insertions, 1 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index eda756556341..c6ea96d5b716 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1849,8 +1849,20 @@ static void unplug_oldest_pwq(struct workqueue_struct *wq)
 	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);
 }