Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Jun 16, 2016 at 01:17:25PM +0200, Petr Mladek wrote:
> +/**
> + * kthread_drain_worker - drain a kthread worker
> + * @worker: worker to be drained
> + *
> + * Wait until there is no work queued for the given kthread worker.
> + * @worker is flushed repeatedly until it becomes empty.  The number
> + * of flushing is determined by the depth of chaining and should
> + * be relatively short.  Whine if it takes too long.
> + *

> + * The caller is responsible for blocking all users of this kthread
> + * worker from queuing new works. Also it is responsible for blocking
> + * the already queued works from an infinite re-queuing!

This, I really dislike that. And it makes the kthread_destroy_worker()
from the next patch unnecessarily fragile.

Why not add a kthread_worker::blocked flag somewhere and refuse/WARN
kthread_queue_work() when that is set.

> + */
> +void kthread_drain_worker(struct kthread_worker *worker)
> +{
> +	int flush_cnt = 0;
> +
> +	spin_lock_irq(&worker->lock);
> +
> +	while (!list_empty(&worker->work_list)) {
> +		spin_unlock_irq(&worker->lock);
> +
> +		kthread_flush_worker(worker);
> +		WARN_ONCE(flush_cnt++ > 10,
> +			  "kthread worker %s: kthread_drain_worker() isn't complete after %u tries\n",
> +			  worker->task->comm, flush_cnt);
> +
> +		spin_lock_irq(&worker->lock);
> +	}
> +
> +	spin_unlock_irq(&worker->lock);
> +}
> +EXPORT_SYMBOL(kthread_drain_worker);
> -- 
> 1.8.5.6
>