wait: Return number of exclusive waiters awaken

Sbitmap code will need to know how many waiters were actually woken for
its batched wakeups implementation.  Return the number of woken
exclusive waiters from __wake_up() to facilitate that.

Suggested-by: Jan Kara <[email protected]>
Signed-off-by: Gabriel Krisman Bertazi <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: krisman

include/linux/wait.h

@@ -209,7 +209,7 @@ __remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq
 	list_del(&wq_entry->entry);
 }
 
-void __wake_up(struct wait_queue_head *wq_head, unsigned int mode, int nr, void *key);
+int __wake_up(struct wait_queue_head *wq_head, unsigned int mode, int nr, void *key);
 void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key);
 void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
 		unsigned int mode, void *key, wait_queue_entry_t *bookmark);

kernel/sched/wait.c

@@ -121,11 +121,12 @@ static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
 	return nr_exclusive;
 }
 
-static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
+static int __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
 			int nr_exclusive, int wake_flags, void *key)
 {
 	unsigned long flags;
 	wait_queue_entry_t bookmark;
+	int remaining = nr_exclusive;
 
 	bookmark.flags = 0;
 	bookmark.private = NULL;
@@ -134,10 +135,12 @@ static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int
 
 	do {
 		spin_lock_irqsave(&wq_head->lock, flags);
-		nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive,
+		remaining = __wake_up_common(wq_head, mode, remaining,
 						wake_flags, key, &bookmark);
 		spin_unlock_irqrestore(&wq_head->lock, flags);
 	} while (bookmark.flags & WQ_FLAG_BOOKMARK);
+
+	return nr_exclusive - remaining;
 }
 
 /**
@@ -147,13 +150,14 @@ static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int
  * @nr_exclusive: how many wake-one or wake-many threads to wake up
  * @key: is directly passed to the wakeup function
  *
- * If this function wakes up a task, it executes a full memory barrier before
- * accessing the task state.
+ * If this function wakes up a task, it executes a full memory barrier
+ * before accessing the task state.  Returns the number of exclusive
+ * tasks that were awaken.
  */
-void __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
-			int nr_exclusive, void *key)
+int __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
+	      int nr_exclusive, void *key)
 {
-	__wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
+	return __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
 }
 EXPORT_SYMBOL(__wake_up);