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>

1 files changed, 7 insertions, 25 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index dd107b83f45f..bc3c18892b7d 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -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);
 }