Re: [RFC PATCH v2 1/2] workqueue: Add warnings and fallback if system_{unbound}_wq is used

[Tejun Heo]

Hello,

On Tue, May 26, 2026 at 05:00:40PM +0200, Marco Crivellari wrote:
> 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
> workqueus are used and redirecting them old used workqueue with the appropriate
> new one.
> 
> Link: https://lore.kernel.org/all/20250221112003.1dSuoGyc@xxxxxxxxxxxxx/
> Suggested-by: Tejun Heo <tj@xxxxxxxxxx>
> Signed-off-by: Marco Crivellari <marco.crivellari@xxxxxxxx>
> ---
>  kernel/workqueue.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 72 insertions(+)
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 33b721a9af02..e17617e205b1 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -2437,6 +2437,24 @@ bool queue_work_on(int cpu, struct workqueue_struct *wq,
>  	bool ret = false;
>  	unsigned long irq_flags;
>  
> +	/*
> +	 * NOTE: These checks are here to assure that no users will still
> +	 * rely on system_wq and system_unbound_wq.
> +	 * They can be removed along with those workqueue when the
> +	 * time comes.
> +	 */
> +	if (unlikely(wq == system_wq)) {

Can you add an internal flag to mark the workqueues and use a helper so that
the warning messages aren't replicated in multiple places? Also, do we need
to have the warning on delayed_queue? Just put it in a single spot where
they'll all converge.

Thanks.

-- 
tejun