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: 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 dd107b8..bc3c188 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -69,7 +69,6 @@
* 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 @@
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 @@
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 @@
*/
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 @@
{
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 @@
mutex_unlock(&wq->mutex);
}
- workqueue_freezing = false;
out_unlock:
mutex_unlock(&wq_pool_mutex);
}