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

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Date:   Wed, 13 Dec 2023 19:32:10 +0100
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Tejun Heo <tj@...nel.org>
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

On 13/12/23 05:35, Tejun Heo wrote:
> 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.

Hummm, don't think we can call that either while the rescuer is actually
running. Maybe we can simply s/kthread_bind_mask/set_cpus_allowed_ptr/
in the above?

Thanks,
Juri