linux-kernel - Re: [PATCH 1/4] workqueue: Reap workers via kthread_stop() and remove detach

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Message-ID: <87ikv28ujk.fsf@linux.ibm.com>
Date: Wed, 11 Sep 2024 10:27:11 +0200
From: "Marc Hartmayer" <mhartmay@...ux.ibm.com>
To: Lai Jiangshan <jiangshanlai@...il.com>
Cc: linux-kernel@...r.kernel.org, Lai Jiangshan
 <jiangshan.ljs@...group.com>,
        Valentin Schneider <vschneid@...hat.com>, Tejun Heo <tj@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Sven
 Schnelle <svens@...ux.ibm.com>, Mete Durlu <meted@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>
Subject: Re: [PATCH 1/4] workqueue: Reap workers via kthread_stop() and
 remove detach_completion

On Wed, Sep 11, 2024 at 11:32 AM +0800, Lai Jiangshan <jiangshanlai@...il.com> wrote:
> On Wed, Sep 11, 2024 at 11:23 AM Lai Jiangshan <jiangshanlai@...il.com> wrote:
>>
>> Hello, Marc
>>

Hi Lai,

[…snip…]

>>
>> I'm not familiar with s390 asm code, but it might be the case that
>> `worker->pool` is NULL in the in worker_thread() since detach_worker()
>> resets worker->pool to NULL.
>>
>> If it is the case, READ_ONCE(worker->pool) should be used in worker_thread()
>> to fix the problem.
>>
>> (It is weird to me if worker->pool is read multi-time in worker_thread()
>> since it is used many times, but since READ_ONCE() is not used, it can
>> be possible).
>
> Oh, it can be possible that the worker is created and then destroyed before
> being waken-up. And if it is the case, READ_ONCE() won't help. I'm going to
> explore if "worker->pool = NULL;" can be moved out from
> detach_worker().

I’ll double check if my assumption is true or not (worker->poll ==
NULL). It may well be that my assumption is wrong.

Thanks for having a look!

>
> Thanks
> Lai
-- 
Kind regards / Beste Grüße
   Marc Hartmayer

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