Re: [PATCH 02/10] workqueue: destroy_worker() should destroy idle workers only

Tejun Heo
2014-05-05T13:13:19Z

Hello,

On Sun, Apr 27, 2014 at 12:08:57PM +0800, Lai Jiangshan wrote:
> @@ -1692,9 +1691,8 @@ static struct worker *alloc_worker(void)
> * create_worker - create a new workqueue worker
> * @pool: pool the new worker will belong to
> *
> - * Create a new worker which is bound to @pool. The returned worker
> - * can be started by calling start_worker() or destroyed using
> - * destroy_worker().
> + * Create a new worker which is bound to @pool.
> + * The new worker should be started and enter idle by start_worker().

Hmm... we used to have a path where a worker is created and then
destroyed without being started. IIRC, it was on the CPU online
failure path. A worker was created for the CPU coming online and if
the online operation failed the created worker was shut down without
being started. Right, we no longer shutdown per-cpu pools on offline
so this doesn't matter anymore. Might worthwhile to note in the patch
description tho.

> @@ -1815,6 +1812,7 @@ static int create_and_start_worker(struct worker_pool *pool)
> * @worker: worker to be destroyed
> *
> * Destroy @worker and adjust @pool stats accordingly.
> + * The worker should be idle(WORKER_IDLE).

Just write "The worker should be idle." Also, in general, can you
please put a space before opening parenthesis?

> *
> * CONTEXT:
> * spin_lock_irq(pool->lock) which is released and regrabbed.
> @@ -1828,13 +1826,13 @@ static void destroy_worker(struct worker *worker)
>
> /* sanity check frenzy */
> if (WARN_ON(worker->current_work) ||
> - WARN_ON(!list_empty(&worker->scheduled)))
> + WARN_ON(!list_empty(&worker->scheduled)) ||
> + WARN_ON(!(worker->flags & WORKER_IDLE)) ||
> + WARN_ON(pool->nr_workers == 1 && !list_empty(&pool->worklist)))

I'm not sure about the pool condition check. It's kinda overreaching
to check for it from worker destruction.

> @@ -3589,6 +3587,7 @@ static void put_unbound_pool(struct worker_pool *pool)
> mutex_lock(&pool->manager_mutex);
> spin_lock_irq(&pool->lock);
>
> + WARN_ON(pool->nr_workers != pool->nr_idle);

Does this condition detect anything new from the condition below?

> while ((worker = first_worker(pool)))
> destroy_worker(worker);
> WARN_ON(pool->nr_workers || pool->nr_idle);

Thanks.

--
tejun