[PATCH v4 0/2] workqueue: Add warnings and check WQ flags usage

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

Hi,

Currently system_wq and system_unbound_wq can still be used and no message
is printed. To avoid further use of them, add a warning. The detection of
deprecated workqueue is done using a new internal flag, called __WQ_DEPRECATED.

Similar scenario for WQ_PERCPU and WQ_UNBOUND. Currently there are still
users that use alloc_workqueue(,0,). To avoid such situations, a couple
of checks have been added:

  - if neither of the flag is present, set WQ_PERCPU
  - if both are present, remove WQ_PERCPU

Along with these, WARN_ONCE() is used.

Thanks!


Marco Crivellari (2):
  workqueue: Add warnings and fallback if system_{unbound}_wq is used
  workqueue: Add warnings and ensure one among WQ_PERCPU or WQ_UNBOUND
    is present

 include/linux/workqueue.h |  1 +
 kernel/workqueue.c        | 31 ++++++++++++++++++++++++++++---
 2 files changed, 29 insertions(+), 3 deletions(-)

---
Changes in v4:
- P2: instead of pr_warn_once() use WARN_ONCE()

Link to v3: https://lore.kernel.org/all/20260528160159.471265-1-marco.crivellari@suse.com/

Changes in v3:
- system_wq / system_unbond_wq not routed to the newer. The warnings have been simpliified
  keeping only one of them inside __queue_work() printing the work function.

- the deprecated status is detected using a new internal flag, called __WQ_DEPRECATED.

Link to v2: https://lore.kernel.org/all/20260526150041.365392-1-marco.crivellari@suse.com/

Changes in v2:
- rebased on v7.1-rc5

- fixed typo in the text

- cleared WQ_PERCPU when wq_pwer_efficient flag is set, to avoid triggering a warning

- if statement to route old workqueue to newer also added in queue_rcu_work()

Link to v1: https://lore.kernel.org/all/20260514092354.125149-1-marco.crivellari@suse.com/

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2.54.0