workqueue: destroy worker directly in the idle timeout handler

Since destroy_worker() doesn't need to sleep nor require manager_mutex,
destroy_worker() can be directly called in the idle timeout
handler, it helps us remove POOL_MANAGE_WORKERS and
maybe_destroy_worker() and simplify the manage_workers()

After POOL_MANAGE_WORKERS is removed, worker_thread() doesn't
need to test whether it needs to manage after processed works.
So we can remove the test branch.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>

kernel/workqueue.c

@@ -68,7 +68,6 @@ enum {
 	 * manager_mutex to avoid changing binding state while
 	 * create_worker() is in progress.
 	 */
-	POOL_MANAGE_WORKERS	= 1 << 0,	/* need to manage workers */
 	POOL_DISASSOCIATED	= 1 << 2,	/* cpu can't serve workers */
 	POOL_FREEZING		= 1 << 3,	/* freeze in progress */
 
@@ -752,13 +751,6 @@ static bool need_to_create_worker(struct worker_pool *pool)
 	return need_more_worker(pool) && !may_start_working(pool);
 }
 
-/* Do I need to be the manager? */
-static bool need_to_manage_workers(struct worker_pool *pool)
-{
-	return need_to_create_worker(pool) ||
-		(pool->flags & POOL_MANAGE_WORKERS);
-}
-
 /* Do we have too many workers and should some go away? */
 static bool too_many_workers(struct worker_pool *pool)
 {
@@ -1868,7 +1860,7 @@ static void idle_worker_timeout(unsigned long __pool)
 
 	spin_lock_irq(&pool->lock);
 
-	if (too_many_workers(pool)) {
+	while (too_many_workers(pool)) {
 		struct worker *worker;
 		unsigned long expires;
 
@@ -1876,13 +1868,12 @@ static void idle_worker_timeout(unsigned long __pool)
 		worker = list_entry(pool->idle_list.prev, struct worker, entry);
 		expires = worker->last_active + IDLE_WORKER_TIMEOUT;
 
-		if (time_before(jiffies, expires))
+		if (time_before(jiffies, expires)) {
 			mod_timer(&pool->idle_timer, expires);
-		else {
-			/* it's been idle for too long, wake up manager */
-			pool->flags |= POOL_MANAGE_WORKERS;
-			wake_up_worker(pool);
+			break;
 		}
+
+		destroy_worker(worker);
 	}
 
 	spin_unlock_irq(&pool->lock);
@@ -2000,44 +1991,6 @@ __acquires(&pool->lock)
 	return true;
 }
 
-/**
- * maybe_destroy_worker - destroy workers which have been idle for a while
- * @pool: pool to destroy workers for
- *
- * Destroy @pool workers which have been idle for longer than
- * IDLE_WORKER_TIMEOUT.
- *
- * LOCKING:
- * spin_lock_irq(pool->lock) which may be released and regrabbed
- * multiple times.  Called only from manager.
- *
- * Return:
- * %false if no action was taken and pool->lock stayed locked, %true
- * otherwise.
- */
-static bool maybe_destroy_workers(struct worker_pool *pool)
-{
-	bool ret = false;
-
-	while (too_many_workers(pool)) {
-		struct worker *worker;
-		unsigned long expires;
-
-		worker = list_entry(pool->idle_list.prev, struct worker, entry);
-		expires = worker->last_active + IDLE_WORKER_TIMEOUT;
-
-		if (time_before(jiffies, expires)) {
-			mod_timer(&pool->idle_timer, expires);
-			break;
-		}
-
-		destroy_worker(worker);
-		ret = true;
-	}
-
-	return ret;
-}
-
 /**
  * manage_workers - manage worker pool
  * @worker: self
@@ -2101,13 +2054,6 @@ static bool manage_workers(struct worker *worker)
 		ret = true;
 	}
 
-	pool->flags &= ~POOL_MANAGE_WORKERS;
-
-	/*
-	 * Destroy and then create so that may_start_working() is true
-	 * on return.
-	 */
-	ret |= maybe_destroy_workers(pool);
 	ret |= maybe_create_worker(pool);
 
 	mutex_unlock(&pool->manager_mutex);
@@ -2349,9 +2295,6 @@ static int worker_thread(void *__worker)
 
 	worker_set_flags(worker, WORKER_PREP, false);
 sleep:
-	if (unlikely(need_to_manage_workers(pool)) && manage_workers(worker))
-		goto recheck;
-
 	/*
 	 * pool->lock is held and there's no work to process and no need to
 	 * manage, sleep.  Workers are woken up only while holding