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>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 189d79b..c458d73 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -163,6 +163,7 @@
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 */
@@ -1688,6 +1689,30 @@
}
/**
+ * 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 @@
* 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 @@
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 @@
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 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 @@
* 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 */