[PATCH v4 1/2] workqueue: Add warnings and fallback if system_{unbound}_wq is used

[Marco Crivellari]

Currently many users transitioned already to the new introduced workqueue
(system_percpu_wq, system_dfl_wq), but there are new users who still use the
older system_wq and system_unbound_wq.

This change try to push this transition forward, by warning whether the old
workqueues are used.

Link: https://lore.kernel.org/all/20250221112003.1dSuoGyc@xxxxxxxxxxxxx/
Suggested-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Marco Crivellari <marco.crivellari@xxxxxxxx>
---
 include/linux/workqueue.h |  1 +
 kernel/workqueue.c        | 12 ++++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 6177624539b3..a283766a192a 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -409,6 +409,7 @@ enum wq_flags {
 	__WQ_DRAINING		= 1 << 16, /* internal: workqueue is draining */
 	__WQ_ORDERED		= 1 << 17, /* internal: workqueue is ordered */
 	__WQ_LEGACY		= 1 << 18, /* internal: create*_workqueue() */
+	__WQ_DEPRECATED		= 1 << 19, /* internal: workqueue is deprecated */
 
 	/* BH wq only allows the following flags */
 	__WQ_BH_ALLOWS		= WQ_BH | WQ_HIGHPRI | WQ_PERCPU,
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 33b721a9af02..0b55f8009eed 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2280,6 +2280,14 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
 	unsigned int work_flags;
 	unsigned int req_cpu = cpu;
 
+	/*
+	 * NOTE: Check whether the used workqueue is deprecated and warn
+	 */
+	if (unlikely(wq->flags & __WQ_DEPRECATED))
+		pr_warn_once("workqueue: work func %ps enqueued on deprecated workqueue. "
+			"Use system_{percpu|dfl}_wq instead.\n",
+			work->func);
+
 	/*
 	 * While a work item is PENDING && off queue, a task trying to
 	 * steal the PENDING will busy-loop waiting for it to either get
@@ -8037,12 +8045,12 @@ void __init workqueue_init_early(void)
 		ordered_wq_attrs[i] = attrs;
 	}
 
-	system_wq = alloc_workqueue("events", WQ_PERCPU, 0);
+	system_wq = alloc_workqueue("events", WQ_PERCPU | __WQ_DEPRECATED, 0);
 	system_percpu_wq = alloc_workqueue("events", WQ_PERCPU, 0);
 	system_highpri_wq = alloc_workqueue("events_highpri",
 					    WQ_HIGHPRI | WQ_PERCPU, 0);
 	system_long_wq = alloc_workqueue("events_long", WQ_PERCPU, 0);
-	system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND, WQ_MAX_ACTIVE);
+	system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND | __WQ_DEPRECATED, WQ_MAX_ACTIVE);
 	system_dfl_wq = alloc_workqueue("events_unbound", WQ_UNBOUND, WQ_MAX_ACTIVE);
 	system_freezable_wq = alloc_workqueue("events_freezable",
 					      WQ_FREEZABLE | WQ_PERCPU, 0);
-- 
2.54.0