linux-kernel - [PATCH] Revert "workqueue: Override implicit ordered attribute in workqueue_apply_unbound

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Date: Mon, 5 Feb 2024 15:43:41 -1000
From: Tejun Heo <tj@...nel.org>
To: Lai Jiangshan <jiangshanlai@...il.com>
Cc: linux-kernel@...r.kernel.org, Waiman Long <longman@...hat.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>
Subject: [PATCH] Revert "workqueue: Override implicit ordered attribute in
 workqueue_apply_unbound_cpumask()"

This reverts commit ca10d851b9ad0338c19e8e3089e24d565ebfffd7.

The commit allowed workqueue_apply_unbound_cpumask() to clear __WQ_ORDERED
on now removed implicitly ordered workqueues. This was incorrect in that
system-wide config change shouldn't break ordering properties of all
workqueues. The reason why apply_workqueue_attrs() path was allowed to do so
was because it was targeting the specific workqueue - either the workqueue
had WQ_SYSFS set or the workqueue user specifically tried to change
max_active, both of which indicate that the workqueue doesn't need to be
ordered.

The implicitly ordered workqueue promotion was removed by the previous
commit 3bc1e711c26b ("workqueue: Don't implicitly make UNBOUND workqueues w/
@max_active==1 ordered"). However, it didn't update this path and broke
build. Let's revert the commit which was incorrect in the first place which
also fixes build.

Signed-off-by: Tejun Heo <tj@...nel.org>
Fixes: 3bc1e711c26b ("workqueue: Don't implicitly make UNBOUND workqueues w/ @max_active==1 ordered")
Cc: stable@...r.kernel.org # v6.6+
---
Applied to wq/for-6.9.

Thanks.

 kernel/workqueue.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ecc775843bfa..cf514ba0dfc3 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -6489,13 +6489,9 @@ static int workqueue_apply_unbound_cpumask(const cpumask_var_t unbound_cpumask)
 	list_for_each_entry(wq, &workqueues, list) {
 		if (!(wq->flags & WQ_UNBOUND) || (wq->flags & __WQ_DESTROYING))
 			continue;
-
 		/* creating multiple pwqs breaks ordering guarantee */
-		if (!list_empty(&wq->pwqs)) {
-			if (wq->flags & __WQ_ORDERED_EXPLICIT)
-				continue;
-			wq->flags &= ~__WQ_ORDERED;
-		}
+		if (wq->flags & __WQ_ORDERED)
+			continue;

 		ctx = apply_wqattrs_prepare(wq, wq->unbound_attrs, unbound_cpumask);
 		if (IS_ERR(ctx)) {
-- 
2.43.0