[PATCH 1/2] workqueue: Make alloc_workqueue() unbound by default

[Marco Crivellari <marco.crivellari@suse.com>]

Currently alloc_workqueue() ensure that one among WQ_PERCPU or WQ_UNBOUND
is present. Now every user has one among these two flags.

In order to achive the future goal of removing WQ_UNBOUND from the code,
start changing the default behavior making alloc_workqueue() act this way:

  - if WQ_PERCPU and WQ_UNBOUND are present: remove WQ_PERCPU (as before)
  - if neither are present: add WQ_UNBOUND

The WARN_ONCE() when neither flags are present has been removed and it has
been replaced by pr_warn_once(): from now on, every alloc_users()
without WQ_PERCPU will be considered unbound.

The pr_warn_once() will be removed along with WQ_UNBOUND in the future.

Link: https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
---
 kernel/workqueue.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1ae3732a2c51..8681343597e8 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5928,16 +5928,16 @@ static struct workqueue_struct *__alloc_workqueue(const char *fmt,
 			     wq->name);
 
 	/*
-	 * One among WQ_PERCPU and WQ_UNBOUND must be set, but not both.
-	 * - If neither is set, default to WQ_PERCPU
-	 * - If both are set, default to WQ_UNBOUND
+	 * Every caller that doesn't explicilty specify WQ_PERCPU will be
+	 * unbound (WQ_UNBOUND) by default.
 	 *
-	 * This code can be removed after workqueue are unbound by default
+	 * If both flags are present at the same time, WQ_PERCPU will be
+	 * removed.
 	 */
 	if (unlikely(!(flags & (WQ_UNBOUND | WQ_PERCPU)))) {
-		WARN_ONCE(1, "workqueue: %s is using neither WQ_PERCPU or WQ_UNBOUND. "
-			  "Setting WQ_PERCPU.\n", wq->name);
-		flags |= WQ_PERCPU;
+		pr_warn_once("workqueue: %s is using neither WQ_PERCPU or WQ_UNBOUND. "
+			  "Setting WQ_UNBOUND.\n", wq->name);
+		flags |= WQ_UNBOUND;
 	} else if (unlikely((flags & WQ_PERCPU) && (flags & WQ_UNBOUND))) {
 		WARN_ONCE(1, "workqueue: %s uses both WQ_PERCPU and WQ_UNBOUND. "
 			  "Dropped WQ_PERCPU, keeping WQ_UNBOUND.\n", wq->name);
-- 
2.55.0