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

[Petr Mladek]

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