* [PATCH v3 1/2] workqueue: Make alloc_workqueue() unbound by default
2026-09-04 14:14 [PATCH v3 0/2] workqueue: Make WQ_UNBOUND the default behavior Marco Crivellari
@ 2026-09-04 14:14 ` Marco Crivellari
2026-09-04 17:01 ` Tejun Heo
2026-09-04 14:14 ` [PATCH v3 2/2] doc: Update WQ_UNBOUND documentation Marco Crivellari
1 sibling, 1 reply; 4+ messages in thread
From: Marco Crivellari @ 2026-09-04 14:14 UTC (permalink / raw)
To: linux-kernel
Cc: Tejun Heo, Lai Jiangshan, Frederic Weisbecker,
Sebastian Andrzej Siewior, Marco Crivellari, Michal Hocko,
Breno Leitao
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been replaced by pr_warn_once(): from now on, every alloc_users()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 | 44 ++++++++++++++++++++++++++++----------------
1 file changed, 28 insertions(+), 16 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1ae3732a2c51..59a43bf1b30d 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5895,12 +5895,33 @@ static struct workqueue_struct *__alloc_workqueue(const char *fmt,
struct workqueue_struct *wq;
size_t wq_size;
int name_len;
+ bool wq_unbound_by_default = false;
+ bool wq_dropped_percpu = false;
if (flags & WQ_BH) {
if (WARN_ON_ONCE(flags & ~__WQ_BH_ALLOWS))
return NULL;
if (WARN_ON_ONCE(max_active))
return NULL;
+ flags |= WQ_PERCPU;
+ }
+
+ /*
+ * Every caller that doesn't explicitly specify WQ_PERCPU will be
+ * unbound (WQ_UNBOUND) by default.
+ *
+ * If both flags are present at the same time, WQ_PERCPU will be
+ * removed.
+ *
+ * This must happen before wq_size is computed below, since that
+ * depends on the finalized WQ_UNBOUND flag.
+ */
+ if (unlikely(!(flags & (WQ_UNBOUND | WQ_PERCPU)))) {
+ flags |= WQ_UNBOUND;
+ wq_unbound_by_default = true;
+ } else if (unlikely((flags & WQ_PERCPU) && (flags & WQ_UNBOUND))) {
+ flags &= ~WQ_PERCPU;
+ wq_dropped_percpu = true;
}
/* see the comment above the definition of WQ_POWER_EFFICIENT */
@@ -5927,22 +5948,13 @@ static struct workqueue_struct *__alloc_workqueue(const char *fmt,
pr_warn_once("workqueue: name exceeds WQ_NAME_LEN. Truncating to: %s\n",
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
- *
- * This code can be removed after workqueue are unbound by default
- */
- 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;
- } 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);
- flags &= ~WQ_PERCPU;
- }
+ if (unlikely(wq_unbound_by_default))
+ pr_warn_once("workqueue: %s is using neither WQ_PERCPU or WQ_UNBOUND. "
+ "Setting WQ_UNBOUND.\n", wq->name);
+
+ WARN_ONCE(wq_dropped_percpu,
+ "workqueue: %s uses both WQ_PERCPU and WQ_UNBOUND. "
+ "Dropped WQ_PERCPU, keeping WQ_UNBOUND.\n", wq->name);
if (flags & WQ_BH) {
/*
--
2.55.0
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH v3 2/2] doc: Update WQ_UNBOUND documentation
2026-09-04 14:14 [PATCH v3 0/2] workqueue: Make WQ_UNBOUND the default behavior Marco Crivellari
2026-09-04 14:14 ` [PATCH v3 1/2] workqueue: Make alloc_workqueue() unbound by default Marco Crivellari
@ 2026-09-04 14:14 ` Marco Crivellari
1 sibling, 0 replies; 4+ messages in thread
From: Marco Crivellari @ 2026-09-04 14:14 UTC (permalink / raw)
To: linux-kernel
Cc: Tejun Heo, Lai Jiangshan, Frederic Weisbecker,
Sebastian Andrzej Siewior, Marco Crivellari, Michal Hocko,
Breno Leitao
When WQ_PERCPU is not present the default behavior is now WQ_UNBOUND,
so update the documentation, reflecting this change.
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>
---
Documentation/core-api/workqueue.rst | 2 ++
1 file changed, 2 insertions(+)
diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst
index bb770f556568..3ca636e065ef 100644
--- a/Documentation/core-api/workqueue.rst
+++ b/Documentation/core-api/workqueue.rst
@@ -206,6 +206,8 @@ resources, scheduled and executed.
* Long running CPU intensive workloads which can be better
managed by the system scheduler.
+ Workqueue without ``WQ_PERCPU`` are unbound by default.
+
``WQ_FREEZABLE``
A freezable wq participates in the freeze phase of the system
suspend operations. Work items on the wq are drained and no
--
2.55.0
^ permalink raw reply [flat|nested] 4+ messages in thread