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From:   "Zhang, Qiang" <Qiang.Zhang@windriver.com>
To:     Lai Jiangshan <jiangshanlai@gmail.com>
CC:     Tejun Heo <tj@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] workqueue: set the rescuer worker that belong to
 freezable wq is freezable
Thread-Topic: [PATCH v2] workqueue: set the rescuer worker that belong to
 freezable wq is freezable
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Date:   Wed, 23 Jun 2021 05:34:15 +0000
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=0A=
=0A=
________________________________________=0A=
From: Lai Jiangshan <jiangshanlai@gmail.com>=0A=
Sent: Wednesday, 23 June 2021 11:16=0A=
To: Zhang, Qiang=0A=
Cc: Tejun Heo; Andrew Morton; LKML=0A=
Subject: Re: [PATCH v2] workqueue: set the rescuer worker that belong to fr=
eezable wq is freezable=0A=
=0A=
[Please note: This e-mail is from an EXTERNAL e-mail address]=0A=
=0A=
On Tue, Jun 22, 2021 at 8:42 PM <qiang.zhang@windriver.com> wrote:=0A=
>=0A=
> From: Zqiang <qiang.zhang@windriver.com>=0A=
>=0A=
> If the rescuer worker belong to freezable wq, when this wq is=0A=
> frozen, the rescuer worker also need to be frozen.=0A=
=0A=
>Hello,=0A=
>=0A=
>From my understanding, the wq subsystem doesn't use >set_freezable(),=0A=
>try_to_freeze() families.  For example, the worker_thread() >doesn't=0A=
>use set_freezable(), neither do in your patch. If kthreads=0A=
>in the wq subsystem need these functions, please let us know.=0A=
>=0A=
>The way the wq subsystem to freeze tasks is by >freeze_workqueues_begin()=
=0A=
>and thaw_workqueues().  When WQs is requested for freezing,=0A=
>they will stop activating work items.  All the workers including=0A=
>*rescuers* will be scheduled as TASK_IDLE when all the >activated work=0A=
>items are processed and the whole wq subsystem is frozen >unless=0A=
>there is any semantic change about TASK_IDLE V.S. "frozen".=0A=
>(rescuers can also only process activated work items.)=0A=
=0A=
Hello Lai=0A=
My understanding is this:=0A=
when the freeze_workqueues_begin() be called, this only set pwq->max_active=
 is zero,   it's just to prevent, after that when we queue the work again, =
we will put it in the pwq->delayed_works,=0A=
but if  there are still some work in the pool->worklist,  the workers in po=
ol are still handle work items, and the rescuer work may be also handle wor=
k items,  until the work items is processed, the workers enters TASK_IDLE s=
tatus.   the rescuer worker is independent of workerpools , when the system=
 freezing,   freeze the rescuer worker directly without waiting for all wor=
kitems to be processed.=0A=
=0A=
Thanks=0A=
Qiang=0A=
=0A=
=0A=
=0A=
=0A=
=0A=
=0A=
=0A=
>=0A=
>Thanks=0A=
>Lai=0A=
=0A=
>=0A=
> Signed-off-by: Zqiang <qiang.zhang@windriver.com>=0A=
> ---=0A=
>  v1->v2:=0A=
>  use kthread_freezable_should_stop() replaces try_to_freeze().=0A=
>=0A=
>  kernel/workqueue.c | 5 ++++-=0A=
>  1 file changed, 4 insertions(+), 1 deletion(-)=0A=
>=0A=
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c=0A=
> index 104e3ef04e33..dd7b78bdb7f1 100644=0A=
> --- a/kernel/workqueue.c=0A=
> +++ b/kernel/workqueue.c=0A=
> @@ -2476,6 +2476,9 @@ static int rescuer_thread(void *__rescuer)=0A=
>          * doesn't participate in concurrency management.=0A=
>          */=0A=
>         set_pf_worker(true);=0A=
> +=0A=
> +       if (wq->flags & WQ_FREEZABLE)=0A=
> +               set_freezable();=0A=
>  repeat:=0A=
>         set_current_state(TASK_IDLE);=0A=
>=0A=
> @@ -2487,7 +2490,7 @@ static int rescuer_thread(void *__rescuer)=0A=
>          * @wq->maydays processing before acting on should_stop so that t=
he=0A=
>          * list is always empty on exit.=0A=
>          */=0A=
> -       should_stop =3D kthread_should_stop();=0A=
> +       should_stop =3D kthread_freezable_should_stop(NULL);=0A=
>=0A=
>         /* see whether any pwq is asking for help */=0A=
>         raw_spin_lock_irq(&wq_mayday_lock);=0A=
> --=0A=
> 2.25.1=0A=
>=0A=