Patch "workqueue: Make wq_adjust_max_active() round-robin pwqs while activating" has been added to the 6.8-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    workqueue: Make wq_adjust_max_active() round-robin pwqs while activating

to the 6.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     workqueue-make-wq_adjust_max_active-round-robin-pwqs.patch
and it can be found in the queue-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 4438a19b7f5e3b95df3793fd71d7e60aa65f45da
Author: Tejun Heo <tj@xxxxxxxxxx>
Date:   Mon Jan 29 08:11:24 2024 -1000

    workqueue: Make wq_adjust_max_active() round-robin pwqs while activating
    
    [ Upstream commit c5404d4e6df6faba1007544b5f4e62c7c14416dd ]
    
    wq_adjust_max_active() needs to activate work items after max_active is
    increased. Previously, it did that by visiting each pwq once activating all
    that could be activated. While this makes sense with per-pwq nr_active,
    nr_active will be shared across multiple pwqs for unbound wqs. Then, we'd
    want to round-robin through pwqs to be fairer.
    
    In preparation, this patch makes wq_adjust_max_active() round-robin pwqs
    while activating. While the activation ordering changes, this shouldn't
    cause user-noticeable behavior changes.
    
    Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
    Reviewed-by: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
    Stable-dep-of: 5797b1c18919 ("workqueue: Implement system-wide nr_active enforcement for unbound workqueues")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 80733046ee012..1659cd4a36c62 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4703,7 +4703,7 @@ static int init_rescuer(struct workqueue_struct *wq)
  */
 static void wq_adjust_max_active(struct workqueue_struct *wq)
 {
-	struct pool_workqueue *pwq;
+	bool activated;
 
 	lockdep_assert_held(&wq->mutex);
 
@@ -4723,19 +4723,26 @@ static void wq_adjust_max_active(struct workqueue_struct *wq)
 	 */
 	WRITE_ONCE(wq->max_active, wq->saved_max_active);
 
-	for_each_pwq(pwq, wq) {
-		unsigned long flags;
-
-		/* this function can be called during early boot w/ irq disabled */
-		raw_spin_lock_irqsave(&pwq->pool->lock, flags);
-
-		while (pwq_activate_first_inactive(pwq))
-			;
+	/*
+	 * Round-robin through pwq's activating the first inactive work item
+	 * until max_active is filled.
+	 */
+	do {
+		struct pool_workqueue *pwq;
 
-		kick_pool(pwq->pool);
+		activated = false;
+		for_each_pwq(pwq, wq) {
+			unsigned long flags;
 
-		raw_spin_unlock_irqrestore(&pwq->pool->lock, flags);
-	}
+			/* can be called during early boot w/ irq disabled */
+			raw_spin_lock_irqsave(&pwq->pool->lock, flags);
+			if (pwq_activate_first_inactive(pwq)) {
+				activated = true;
+				kick_pool(pwq->pool);
+			}
+			raw_spin_unlock_irqrestore(&pwq->pool->lock, flags);
+		}
+	} while (activated);
 }
 
 __printf(1, 4)