workqueue: async worker destruction

worker destruction includes these parts of code:
	adjust pool's stats
	remove the worker from idle list
	detach the worker from the pool
	kthread_stop() to wait for the worker's task exit
	free the worker struct

We can find out that there is no essential work to do after
kthread_stop(), which means destroy_worker() doesn't need to wait for
the worker's task exit, so we can remove kthread_stop() and free the
worker struct in the worker exiting path.

However, put_unbound_pool() still needs to sync the all the workers'
destruction before destroying the pool; otherwise, the workers may
access to the invalid pool when they are exiting.

So we also move the code of "detach the worker" to the exiting
path and let put_unbound_pool() to sync with this code via
detach_completion.

The code of "detach the worker" is wrapped in a new function
"worker_detach_from_pool()" although worker_detach_from_pool() is only
called once (in worker_thread()) after this patch, but we need to wrap
it for these reasons:

  1) The code of "detach the worker" is not short enough to unfold them
     in worker_thread().
  2) the name of "worker_detach_from_pool()" is self-comment, and we add
     some comments above the function.
  3) it will be shared by rescuer in later patch which allows rescuer
     and normal thread use the same attach/detach frameworks.

The worker id is freed when detaching which happens before the worker
is fully dead, but this id of the dying worker may be re-used for a
new worker, so the dying worker's task name is changed to
"worker/dying" to avoid two or several workers having the same name.

Since "detach the worker" is moved out from destroy_worker(),
destroy_worker() doesn't require manager_mutex, so the
"lockdep_assert_held(&pool->manager_mutex)" in destroy_worker() is
removed, and destroy_worker() is not protected by manager_mutex in
put_unbound_pool().

tj: Minor description updates.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Lai Jiangshan 2014-05-20 17:46:29 +08:00 committed by Tejun Heo
parent 73eb7fe73a
commit 60f5a4bcf8

View File

@ -163,6 +163,7 @@ struct worker_pool {
struct mutex manager_arb; /* manager arbitration */
struct mutex manager_mutex; /* manager exclusion */
struct idr worker_idr; /* M: worker IDs and iteration */
struct completion *detach_completion; /* all workers detached */
struct workqueue_attrs *attrs; /* I: worker attributes */
struct hlist_node hash_node; /* PL: unbound_pool_hash node */
@ -1687,6 +1688,30 @@ static struct worker *alloc_worker(void)
return worker;
}
/**
* worker_detach_from_pool() - detach a worker from its pool
* @worker: worker which is attached to its pool
* @pool: the pool @worker is attached to
*
* Undo the attaching which had been done in create_worker(). The caller
* worker shouldn't access to the pool after detached except it has other
* reference to the pool.
*/
static void worker_detach_from_pool(struct worker *worker,
struct worker_pool *pool)
{
struct completion *detach_completion = NULL;
mutex_lock(&pool->manager_mutex);
idr_remove(&pool->worker_idr, worker->id);
if (idr_is_empty(&pool->worker_idr))
detach_completion = pool->detach_completion;
mutex_unlock(&pool->manager_mutex);
if (detach_completion)
complete(detach_completion);
}
/**
* create_worker - create a new workqueue worker
* @pool: pool the new worker will belong to
@ -1815,13 +1840,12 @@ static int create_and_start_worker(struct worker_pool *pool)
* be idle.
*
* CONTEXT:
* spin_lock_irq(pool->lock) which is released and regrabbed.
* spin_lock_irq(pool->lock).
*/
static void destroy_worker(struct worker *worker)
{
struct worker_pool *pool = worker->pool;
lockdep_assert_held(&pool->manager_mutex);
lockdep_assert_held(&pool->lock);
/* sanity check frenzy */
@ -1833,24 +1857,9 @@ static void destroy_worker(struct worker *worker)
pool->nr_workers--;
pool->nr_idle--;
/*
* Once WORKER_DIE is set, the kworker may destroy itself at any
* point. Pin to ensure the task stays until we're done with it.
*/
get_task_struct(worker->task);
list_del_init(&worker->entry);
worker->flags |= WORKER_DIE;
idr_remove(&pool->worker_idr, worker->id);
spin_unlock_irq(&pool->lock);
kthread_stop(worker->task);
put_task_struct(worker->task);
kfree(worker);
spin_lock_irq(&pool->lock);
wake_up_process(worker->task);
}
static void idle_worker_timeout(unsigned long __pool)
@ -2289,6 +2298,10 @@ woke_up:
spin_unlock_irq(&pool->lock);
WARN_ON_ONCE(!list_empty(&worker->entry));
worker->task->flags &= ~PF_WQ_WORKER;
set_task_comm(worker->task, "kworker/dying");
worker_detach_from_pool(worker, pool);
kfree(worker);
return 0;
}
@ -3560,6 +3573,7 @@ static void rcu_free_pool(struct rcu_head *rcu)
*/
static void put_unbound_pool(struct worker_pool *pool)
{
DECLARE_COMPLETION_ONSTACK(detach_completion);
struct worker *worker;
lockdep_assert_held(&wq_pool_mutex);
@ -3583,15 +3597,21 @@ static void put_unbound_pool(struct worker_pool *pool)
* manager_mutex.
*/
mutex_lock(&pool->manager_arb);
mutex_lock(&pool->manager_mutex);
spin_lock_irq(&pool->lock);
spin_lock_irq(&pool->lock);
while ((worker = first_worker(pool)))
destroy_worker(worker);
WARN_ON(pool->nr_workers || pool->nr_idle);
spin_unlock_irq(&pool->lock);
mutex_lock(&pool->manager_mutex);
if (!idr_is_empty(&pool->worker_idr))
pool->detach_completion = &detach_completion;
mutex_unlock(&pool->manager_mutex);
if (pool->detach_completion)
wait_for_completion(pool->detach_completion);
mutex_unlock(&pool->manager_arb);
/* shut down the timers */