回复: [PATCH v4] kthread: Work could not be queued when worker being destroyed

[Zhang, Qiang]

Sorry,  Pter Mladek, this is my mistake please ignore this change.

________________________________________
发件人: linux-kernel-owner@xxxxxxxxxxxxxxx <linux-kernel-owner@xxxxxxxxxxxxxxx> 代表 Petr Mladek <pmladek@xxxxxxxx>
发送时间: 2020年7月7日 17:06
收件人: Zhang, Qiang
抄送: ben.dooks@xxxxxxxxxxxxxxx; bfields@xxxxxxxxxx; cl@xxxxxxxxxxxxxx; peterz@xxxxxxxxxxxxx; tj@xxxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx; naresh.kamboju@xxxxxxxxxx; mm-commits@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
主题: Re: [PATCH v4] kthread: Work could not be queued when worker being destroyed

On Mon 2020-07-06 13:46:47, qiang.zhang@xxxxxxxxxxxxx wrote:
> From: Zhang Qiang <qiang.zhang@xxxxxxxxxxxxx>
>
> Before the work is put into the queue of the worker thread,
> the state of the worker thread needs to be detected,because
> the worker thread may be in the destruction state at this time.
>
> Signed-off-by: Zhang Qiang <qiang.zhang@xxxxxxxxxxxxx>
> Suggested-by: Petr Mladek <pmladek@xxxxxxxx>
> Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>

This patch is completely different from the one that I suggested
or acked. Please, never keep acks when doing major rework and
people did not agree with it.

For this patch:

Nacked-by: Petr Mladek <pmladek@xxxxxxxx>

See below why.


> ---
>  v1->v2:
>  Add warning information for condition "!worker->task".
>  v2->v3:
>  Modify submission information and add "Reviewed-by" tags.
>  v3->v4:
>  Fix spi controller register trigger Warning.
>  when a spi controller register, a "kthread_worker_fn" worker is created
>  through "kthread_run" instead of "kthread_create_worker" which in this
>  func the "worker->task" will be initialized. and then the "spi_start_queue"
>  func queue a work to worker queue, at this time, if the worker has not
>  begin to running, the "!worker->task" will be true, so a warning is triggered.
>
>  kernel/kthread.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index bfbfa481be3a..825bd4dcdb95 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -791,6 +791,11 @@ static inline bool queuing_blocked(struct kthread_worker *worker,
>  {
>       lockdep_assert_held(&worker->lock);
>
> +     if (kthread_should_stop()) {

This does not make much sense.

kthread_should_stop() checks a flag set for the "current" process.
It works only when called from inside the kthread worker thread.

queuing_blocked() is called from kthread_queue_work()
or kthread_queue_delayed_work(). These are typically
called from another process. The only exception is when
they get re-queued from inside the work.

Best Regards,
Petr


> +             WARN_ON(1);
> +             return true;
> +     }
> +
>       return !list_empty(&work->node) || work->canceling;
>  }
>
> --
> 2.24.1