linux-kernel - Re: [RFC PATCH 0/2] workqueue: Introduce PF_WQ_RESCUE

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Date:   Wed, 13 Dec 2023 05:35:50 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     Aaron Tomlin <atomlin@...mlin.com>, linux-kernel@...r.kernel.org,
        jiangshanlai@...il.com, peterz@...radead.org
Subject: Re: [RFC PATCH 0/2] workqueue: Introduce PF_WQ_RESCUE_WORKER

Hello,

On Wed, Dec 13, 2023 at 09:59:42AM +0100, Juri Lelli wrote:
> Something like the following then maybe?
> 
> ---
>  kernel/workqueue.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 2989b57e154a7..ed73f7f80d57d 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -4405,6 +4405,12 @@ static void apply_wqattrs_commit(struct apply_wqattrs_ctx *ctx)
>         link_pwq(ctx->dfl_pwq);
>         swap(ctx->wq->dfl_pwq, ctx->dfl_pwq);
> 
> +       /* rescuer needs to respect wq cpumask changes */
> +       if (ctx->wq->rescuer) {
> +               kthread_bind_mask(ctx->wq->rescuer->task, ctx->attrs->cpumask);
> +               wake_up_process(ctx->wq->rescuer->task);
> +       }
> +
>         mutex_unlock(&ctx->wq->mutex);
>  }

I'm not sure kthread_bind_mask() would be safe here. The rescuer might be
running a work item. wait_task_inactive() might fail and we don't want to
change cpumask while the rescuer is active anyway.

Maybe the easiest way to do this is making rescuer_thread() restore the wq's
cpumask right before going to sleep, and making apply_wqattrs_commit() just
wake up the rescuer.

Thanks.

-- 
tejun