Re: [PATCH v3 1/2] workqueue: Add warnings and fallback if system_{unbound}_wq is used

[Breno Leitao <leitao@debian.org>]

On Thu, May 28, 2026 at 06:01:58PM +0000, 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.
> 
> 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>
> ---
>  include/linux/workqueue.h |  1 +
>  kernel/workqueue.c        | 12 ++++++++++--
>  2 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
> index 6177624539b3..a283766a192a 100644
> --- a/include/linux/workqueue.h
> +++ b/include/linux/workqueue.h
> @@ -409,6 +409,7 @@ enum wq_flags {
>  	__WQ_DRAINING		= 1 << 16, /* internal: workqueue is draining */
>  	__WQ_ORDERED		= 1 << 17, /* internal: workqueue is ordered */
>  	__WQ_LEGACY		= 1 << 18, /* internal: create*_workqueue() */
> +	__WQ_DEPRECATED		= 1 << 19, /* internal: workqueue is deprecated */
>  
>  	/* BH wq only allows the following flags */
>  	__WQ_BH_ALLOWS		= WQ_BH | WQ_HIGHPRI | WQ_PERCPU,
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 33b721a9af02..0b55f8009eed 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -2280,6 +2280,14 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
>  	unsigned int work_flags;
>  	unsigned int req_cpu = cpu;
>  
> +	/*
> +	 * NOTE: Check whether the used workqueue is deprecated and warn
> +	 */
> +	if (unlikely(wq->flags & __WQ_DEPRECATED))
> +		pr_warn_once("workqueue: work func %ps enqueued on deprecated workqueue. "
> +			"Use system_{percpu|dfl}_wq instead.\n",
> +			work->func);

Silly question, can we make this a build warning?