X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=kernel%2Fworkqueue.c;h=61bcf37808ed1f16e479dad52399240b7da3ee42;hb=f5118000d9554862b2b37bd220a2f8b1b47cea73;hp=a2c7e437796039b7e24fc992222379486b9a1d9c;hpb=77917ecac9c37f9f02e7954b617df8f824894778;p=firefly-linux-kernel-4.4.55.git

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a2c7e4377960..61bcf37808ed 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1947,17 +1947,13 @@ static void pool_mayday_timeout(unsigned long __pool)
  * spin_lock_irq(pool->lock) which may be released and regrabbed
  * multiple times.  Does GFP_KERNEL allocations.  Called only from
  * manager.
- *
- * RETURNS:
- * %false if no action was taken and pool->lock stayed locked, %true
- * otherwise.
  */
-static bool maybe_create_worker(struct worker_pool *pool)
+static void maybe_create_worker(struct worker_pool *pool)
 __releases(&pool->lock)
 __acquires(&pool->lock)
 {
 	if (!need_to_create_worker(pool))
-		return false;
+		return;
 restart:
 	spin_unlock_irq(&pool->lock);
 
@@ -1974,7 +1970,7 @@ restart:
 			start_worker(worker);
 			if (WARN_ON_ONCE(need_to_create_worker(pool)))
 				goto restart;
-			return true;
+			return;
 		}
 
 		if (!need_to_create_worker(pool))
@@ -1991,7 +1987,7 @@ restart:
 	spin_lock_irq(&pool->lock);
 	if (need_to_create_worker(pool))
 		goto restart;
-	return true;
+	return;
 }
 
 /**
@@ -2004,15 +2000,9 @@ restart:
  * LOCKING:
  * spin_lock_irq(pool->lock) which may be released and regrabbed
  * multiple times.  Called only from manager.
- *
- * RETURNS:
- * %false if no action was taken and pool->lock stayed locked, %true
- * otherwise.
  */
-static bool maybe_destroy_workers(struct worker_pool *pool)
+static void maybe_destroy_workers(struct worker_pool *pool)
 {
-	bool ret = false;
-
 	while (too_many_workers(pool)) {
 		struct worker *worker;
 		unsigned long expires;
@@ -2026,10 +2016,7 @@ static bool maybe_destroy_workers(struct worker_pool *pool)
 		}
 
 		destroy_worker(worker);
-		ret = true;
 	}
-
-	return ret;
 }
 
 /**
@@ -2049,13 +2036,14 @@ static bool maybe_destroy_workers(struct worker_pool *pool)
  * multiple times.  Does GFP_KERNEL allocations.
  *
  * RETURNS:
- * spin_lock_irq(pool->lock) which may be released and regrabbed
- * multiple times.  Does GFP_KERNEL allocations.
+ * %false if the pool doesn't need management and the caller can safely
+ * start processing works, %true if management function was performed and
+ * the conditions that the caller verified before calling the function may
+ * no longer be true.
  */
 static bool manage_workers(struct worker *worker)
 {
 	struct worker_pool *pool = worker->pool;
-	bool ret = false;
 
 	/*
 	 * Managership is governed by two mutexes - manager_arb and
@@ -2079,7 +2067,7 @@ static bool manage_workers(struct worker *worker)
 	 * manager_mutex.
 	 */
 	if (!mutex_trylock(&pool->manager_arb))
-		return ret;
+		return false;
 
 	/*
 	 * With manager arbitration won, manager_mutex would be free in
@@ -2089,7 +2077,6 @@ static bool manage_workers(struct worker *worker)
 		spin_unlock_irq(&pool->lock);
 		mutex_lock(&pool->manager_mutex);
 		spin_lock_irq(&pool->lock);
-		ret = true;
 	}
 
 	pool->flags &= ~POOL_MANAGE_WORKERS;
@@ -2098,12 +2085,12 @@ static bool manage_workers(struct worker *worker)
 	 * Destroy and then create so that may_start_working() is true
 	 * on return.
 	 */
-	ret |= maybe_destroy_workers(pool);
-	ret |= maybe_create_worker(pool);
+	maybe_destroy_workers(pool);
+	maybe_create_worker(pool);
 
 	mutex_unlock(&pool->manager_mutex);
 	mutex_unlock(&pool->manager_arb);
-	return ret;
+	return true;
 }
 
 /**
@@ -2887,19 +2874,57 @@ bool flush_work(struct work_struct *work)
 }
 EXPORT_SYMBOL_GPL(flush_work);
 
+struct cwt_wait {
+	wait_queue_t		wait;
+	struct work_struct	*work;
+};
+
+static int cwt_wakefn(wait_queue_t *wait, unsigned mode, int sync, void *key)
+{
+	struct cwt_wait *cwait = container_of(wait, struct cwt_wait, wait);
+
+	if (cwait->work != key)
+		return 0;
+	return autoremove_wake_function(wait, mode, sync, key);
+}
+
 static bool __cancel_work_timer(struct work_struct *work, bool is_dwork)
 {
+	static DECLARE_WAIT_QUEUE_HEAD(cancel_waitq);
 	unsigned long flags;
 	int ret;
 
 	do {
 		ret = try_to_grab_pending(work, is_dwork, &flags);
 		/*
-		 * If someone else is canceling, wait for the same event it
-		 * would be waiting for before retrying.
+		 * If someone else is already canceling, wait for it to
+		 * finish.  flush_work() doesn't work for PREEMPT_NONE
+		 * because we may get scheduled between @work's completion
+		 * and the other canceling task resuming and clearing
+		 * CANCELING - flush_work() will return false immediately
+		 * as @work is no longer busy, try_to_grab_pending() will
+		 * return -ENOENT as @work is still being canceled and the
+		 * other canceling task won't be able to clear CANCELING as
+		 * we're hogging the CPU.
+		 *
+		 * Let's wait for completion using a waitqueue.  As this
+		 * may lead to the thundering herd problem, use a custom
+		 * wake function which matches @work along with exclusive
+		 * wait and wakeup.
 		 */
-		if (unlikely(ret == -ENOENT))
-			flush_work(work);
+		if (unlikely(ret == -ENOENT)) {
+			struct cwt_wait cwait;
+
+			init_wait(&cwait.wait);
+			cwait.wait.func = cwt_wakefn;
+			cwait.work = work;
+
+			prepare_to_wait_exclusive(&cancel_waitq, &cwait.wait,
+						  TASK_UNINTERRUPTIBLE);
+			if (work_is_canceling(work))
+				schedule();
+			finish_wait(&cancel_waitq, &cwait.wait);
+		}
 	} while (unlikely(ret < 0));
 
 	/* tell other tasks trying to grab @work to back off */
@@ -2908,6 +2933,16 @@ static bool __cancel_work_timer(struct work_struct *work, bool is_dwork)
 
 	flush_work(work);
 	clear_work_data(work);
+
+	/*
+	 * Paired with prepare_to_wait() above so that either
+	 * waitqueue_active() is visible here or !work_is_canceling() is
+	 * visible there.
+	 */
+	smp_mb();
+	if (waitqueue_active(&cancel_waitq))
+		__wake_up(&cancel_waitq, TASK_NORMAL, 1, work);
+
 	return ret;
 }