[RFC PATCH 2/8] workqueue: Make create_worker() safe against prematurely wakeups

[Hillf Danton <hdanton@sina.com>]

On Thu,  4 Aug 2022 16:41:29 +0800 Lai Jiangshan wrote:
>  
> @@ -1942,6 +1943,7 @@ static struct worker *create_worker(struct worker_pool *pool)
>  		goto fail;
>  
>  	worker->id = id;
> +	worker->pool = pool;
>  
>  	if (pool->cpu >= 0)
>  		snprintf(id_buf, sizeof(id_buf), "%d:%d%s", pool->cpu, id,
> @@ -1949,6 +1951,7 @@ static struct worker *create_worker(struct worker_pool *pool)
>  	else
>  		snprintf(id_buf, sizeof(id_buf), "u%d:%d", pool->id, id);
>  
> +	reinit_completion(&pool->created);
>  	worker->task = kthread_create_on_node(worker_thread, worker, pool->node,
>  					      "kworker/%s", id_buf);
>  	if (IS_ERR(worker->task))
> @@ -1957,15 +1960,9 @@ static struct worker *create_worker(struct worker_pool *pool)
>  	set_user_nice(worker->task, pool->attrs->nice);
>  	kthread_bind_mask(worker->task, pool->attrs->cpumask);
>  
> -	/* successful, attach the worker to the pool */
> -	worker_attach_to_pool(worker, pool);
> -
>  	/* start the newly created worker */
> -	raw_spin_lock_irq(&pool->lock);
> -	worker->pool->nr_workers++;
> -	worker_enter_idle(worker);
>  	wake_up_process(worker->task);
> -	raw_spin_unlock_irq(&pool->lock);
> +	wait_for_completion(&pool->created);
>  
>  	return worker;

	cpu0	cpu1		cpu2
	===	===		===
		complete

	reinit_completion
				wait_for_completion

Any chance for race above?