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Commit 74b414ea authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Tejun Heo
Browse files

workqueue: remove the confusing POOL_FREEZING 



Currently, the global freezing state is propagated to worker_pools via
POOL_FREEZING and then to each workqueue; however, the middle step -
propagation through worker_pools - can be skipped as long as one or
more max_active adjustments happens for each workqueue after the
update to the global state is visible.  The global workqueue freezing
state and the max_active adjustments during workqueue creation and
[un]freezing are serialized with wq_pool_mutex, so it's trivial to
guarantee that max_actives stay in sync with global freezing state.

POOL_FREEZING is unnecessary and makes the code more confusing and
complicates freeze_workqueues_begin() and thaw_workqueues() by
requiring them to walk through all pools.

Remove POOL_FREEZING and use workqueue_freezing directly instead.

tj: Description and comment updates.

Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 1037de36

kernel/workqueue.c

+7 −25
Original line number Diff line number Diff line
@@ -69,7 +69,6 @@ enum { 
	 * worker_attach_to_pool() is in progress.

	 */

	POOL_DISASSOCIATED	= 1 << 2,	/* cpu can't serve workers */

	POOL_FREEZING		= 1 << 3,	/* freeze in progress */



	/* worker flags */

	WORKER_DIE		= 1 << 1,	/* die die die */
@@ -3533,9 +3532,6 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs) 
	if (!pool || init_worker_pool(pool) < 0)

		goto fail;



	if (workqueue_freezing)

		pool->flags |= POOL_FREEZING;



	lockdep_set_subclass(&pool->lock, 1);	/* see put_pwq() */

	copy_workqueue_attrs(pool->attrs, attrs);
@@ -3642,7 +3638,12 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq) 


	spin_lock_irq(&pwq->pool->lock);



	if (!freezable || !(pwq->pool->flags & POOL_FREEZING)) {

	/*

	 * During [un]freezing, the caller is responsible for ensuring that

	 * this function is called at least once after @workqueue_freezing

	 * is updated and visible.

	 */

	if (!freezable || !workqueue_freezing) {

		pwq->max_active = wq->saved_max_active;



		while (!list_empty(&pwq->delayed_works) &&
@@ -4751,24 +4752,14 @@ EXPORT_SYMBOL_GPL(work_on_cpu); 
 */

void freeze_workqueues_begin(void)

{

	struct worker_pool *pool;

	struct workqueue_struct *wq;

	struct pool_workqueue *pwq;

	int pi;



	mutex_lock(&wq_pool_mutex);



	WARN_ON_ONCE(workqueue_freezing);

	workqueue_freezing = true;



	/* set FREEZING */

	for_each_pool(pool, pi) {

		spin_lock_irq(&pool->lock);

		WARN_ON_ONCE(pool->flags & POOL_FREEZING);

		pool->flags |= POOL_FREEZING;

		spin_unlock_irq(&pool->lock);

	}



	list_for_each_entry(wq, &workqueues, list) {

		mutex_lock(&wq->mutex);

		for_each_pwq(pwq, wq)
@@ -4838,21 +4829,13 @@ void thaw_workqueues(void) 
{

	struct workqueue_struct *wq;

	struct pool_workqueue *pwq;

	struct worker_pool *pool;

	int pi;



	mutex_lock(&wq_pool_mutex);



	if (!workqueue_freezing)

		goto out_unlock;



	/* clear FREEZING */

	for_each_pool(pool, pi) {

		spin_lock_irq(&pool->lock);

		WARN_ON_ONCE(!(pool->flags & POOL_FREEZING));

		pool->flags &= ~POOL_FREEZING;

		spin_unlock_irq(&pool->lock);

	}

	workqueue_freezing = false;



	/* restore max_active and repopulate worklist */

	list_for_each_entry(wq, &workqueues, list) {
@@ -4862,7 +4845,6 @@ void thaw_workqueues(void) 
		mutex_unlock(&wq->mutex);

	}



	workqueue_freezing = false;

out_unlock:

	mutex_unlock(&wq_pool_mutex);

}