Re: [PATCH 1/9] workqueue: devres: Add device-managed allocate workqueue

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

+Cc: devm-helpers maintainers/reviewers

On Mon, Feb 23, 2026 at 12:52:14PM +0100, Krzysztof Kozlowski wrote:
> On 23/02/2026 09:56, Andy Shevchenko wrote:
> > On Mon, Feb 23, 2026 at 08:27:29AM +0100, Krzysztof Kozlowski wrote:
> >> Add a Resource-managed version of alloc_workqueue() to fix common
> >> problem of drivers mixing devm() calls with destroy_workqueue.  Such
> >> naive and discouraged driver approach leads to difficult to debug bugs
> >> when the driver:
> >>
> >> 1. Allocates workqueue in standard way and destroys it in driver
> >>    remove() callback,
> >> 2. Sets work struct with devm_work_autocancel(),
> >> 3. Registers interrupt handler with devm_request_threaded_irq().
> >>
> >> Which leads to following unbind/removal path:
> >>
> >> 1. destroy_workqueue() via driver remove(),
> >>    Any interrupt coming now would still execute the interrupt handler,
> >>    which queues work on destroyed workqueue.
> >> 2. devm_irq_release(),
> >> 3. devm_work_drop() -> cancel_work_sync() on destroyed workqueue.
> >>
> >> devm_alloc_workqueue() has two benefits:
> >> 1. Solves above problem of mix-and-match devres and non-devres code in
> >>    driver,
> >> 2. Simplify any sane drivers which were correctly using
> >>    alloc_workqueue() + devm_add_action_or_reset().
> > 
> >>  include/linux/workqueue.h                        | 32 ++++++++++++++++++++++++
> >>  kernel/workqueue.c                               | 32 ++++++++++++++++++++++++
> > 
> > Hmm... We have devm-helpers.h. Why the new one is in workqueue.h?
> > Can we have some consistency here?
> 
> Answering with update:
> I don't think this should go to devm-helpers.h. The definition is in
> workqueue.c, thus the declaration should be in corresponding header.
> It's logical and consistent.
> 
> Otherwise, I could move it entirely - definition and declaration - to
> devm-helpers.h, but then the release (devm_destroy_workqueue()) will be
> essentially exported to everyone through the header.
> 
> So kind of conflicting choices.

Hmm... An alternative I see is more intrusive but should make it less
inconsistent: Treat the devm-helpers as devres like header for workqueue
and collect there all devm_*wq* related stuff with maybe something putting
back to / holding in the c-file.

OTOH we may leave devm_destroy_workqueue() visible for now with a comment
saying do not use, it's internal or something like that.

Hans, what would be your opinion as you IIRC is the author of devm-helpers.h?

Matti, I also Cc'ed to you, you have usually non-standard thinkig and
insightful solutions (besides being reviewer of devm-helpers).

-- 
With Best Regards,
Andy Shevchenko