Re: [PATCH 1/4] workqueue: Reap workers via kthread_stop() and remove detach_completion

[Marc Hartmayer]

On Wed, Sep 11, 2024 at 10:27 AM +0200, "Marc Hartmayer" <mhartmay@xxxxxxxxxxxxx> wrote:
> On Wed, Sep 11, 2024 at 11:32 AM +0800, Lai Jiangshan <jiangshanlai@xxxxxxxxx> wrote:
>> On Wed, Sep 11, 2024 at 11:23 AM Lai Jiangshan <jiangshanlai@xxxxxxxxx> 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.

I applied the following patch on top of commit bc83b4d1f086 ("Merge tag
'bcachefs-2024-09-09' of git://evilpiepirate.org/bcachefs")