Re: [PATCH 04/10] workqueue: destroy worker directly in the idle timeout handler

Lai Jiangshan
2014-05-07T07:06:14Z

On 05/05/2014 10:36 PM, Tejun Heo wrote:
> On Sun, Apr 27, 2014 at 12:08:59PM +0800, Lai Jiangshan wrote:
>> Since kthread_stop() is removed from destroy_worker(),
>> destroy_worker() doesn't need to sleep.
>> Since "unbind the worker" is moved out from destroy_worker(),
>> destroy_worker() doesn't require manager_mutex.
>>
>> So destroy_worker() can be directly called in the idle timeout
>> handler, it helps us remove POOL_MANAGE_WORKERS and
>> maybe_destroy_worker() and simplify the manage_workers()
>>
>> After POOL_MANAGE_WORKERS is removed, worker_thread() doesn't
>> need to test whether it needs to manage after processed works.
>> So we can remove this test branch.
>
> Ah, so, you can take out workers directly from idle timer. Yeah,
> that's nice. I'm not a big fan of the wait_queue usage in the
> previous patch tho. Can we use a completion instead?
>
> Thanks.
>

1) complete() can't be called inside attach_mutex due to the worker
shouldn't access to the pool after complete().
2) put_unbound_pool() may called from get_unbound_pool(), we need to add
an additional check and avoid the wait_for_completion() if so.

+static void worker_detach_from_pool(struct worker *worker, struct worker_pool *pool)
+{
+ bool is_last;
+
+ mutex_lock(&pool->bind_mutex);
+ list_del(&worker->bind_entry);
+ is_last = list_empty(&worker->bind_entry);
+ mutex_unlock(&pool->bind_mutex);
+
+ /* need some comments here */
+ if (is_last)
+ complete(&pool->workers_detached);
+}

@@ -3588,6 +3587,7 @@ static void put_unbound_pool(struct worker_pool *pool)
mutex_lock(&pool->manager_mutex);
spin_lock_irq(&pool->lock);

+ need_to_wait = pool->nr_workers != 0; /* it may be called from get_unbound_pool() */
while ((worker = first_worker(pool)))
destroy_worker(worker);
WARN_ON(pool->nr_workers || pool->nr_idle);
@@ -3596,6 +3596,8 @@ static void put_unbound_pool(struct worker_pool *pool)
mutex_unlock(&pool->manager_mutex);
mutex_unlock(&pool->manager_arb);

+ if (need_to_wait)
+ wait_for_completion(&pool->workers_detached);

/* shut down the timers */
del_timer_sync(&pool->idle_timer);
del_timer_sync(&pool->mayday_timer);

So I think wait_queue is more grace.

Thanks,
Lai