[PATCH v4 0/2] workqueue: Make WQ_UNBOUND the default behavior

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

Hi,

Currently alloc_workqueue() make sure one among WQ_UNBOUND or WQ_PERCPU is
present. This is enforced warning and setting WQ_PERCPU as default when
alloc_workqueue() without WQ_PERCPU or WQ_UNBOUND.

[ P1 ] change this behavior: if no flags are specified, WQ_UNBOUND is
set by default, changing the default behavior when flags are not present.

WQ_BH is always per-CPU, so WQ_PERCPU is forced in case it is not present.

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been replaced by pr_warn_once(): from now on, every alloc_users()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.

Q: I decided to pr_warn_once() just to make sure users are aware of the new
behavior. It makes sense or we can just drop it directly?
I don't think the WARN_ONCE() is appropriate now, for this specific path.

[ P2 ] updates the documentation accordingly.

Thanks!

---
Changes in v4:
- WQ_BH: add documentation about BH workqueue implying WQ_PERCPU

Link to v3: https://lore.kernel.org/all/20260904141421.287647-1-marco.crivellari@suse.com/

Changes in v3:
- WQ_BH require WQ_PERCPU

Link to v2: https://lore.kernel.org/all/20260903165251.481362-1-marco.crivellari@suse.com/

Changes in v2:
- if/else to add/drop WQ_UNBOUND/WQ_PERCPU moved before wq_size assignment

Link to v1: https://lore.kernel.org/all/20260903152204.401638-1-marco.crivellari@suse.com/

Marco Crivellari (2):
  workqueue: Make alloc_workqueue() unbound by default
  doc: Update WQ_UNBOUND and WQ_BH documentation

 Documentation/core-api/workqueue.rst |  9 ++++--
 kernel/workqueue.c                   | 44 ++++++++++++++++++----------
 2 files changed, 35 insertions(+), 18 deletions(-)

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2.55.0