sched: remove wait bookmarks

There are no users of wait bookmarks left, so simplify the wait
code by removing them.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Cc: Benjamin Segall <[email protected]>
Cc: Bin Lai <[email protected]>
Cc: Daniel Bristot de Oliveira <[email protected]>
Cc: Dietmar Eggemann <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Juri Lelli <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Steven Rostedt (Google) <[email protected]>
Cc: Valentin Schneider <[email protected]>
Cc: Vincent Guittot <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Matthew Wilcox (Oracle)

include/linux/wait.h

@@ -19,10 +19,9 @@ int default_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int
 /* wait_queue_entry::flags */
 #define WQ_FLAG_EXCLUSIVE	0x01
 #define WQ_FLAG_WOKEN		0x02
-#define WQ_FLAG_BOOKMARK	0x04
-#define WQ_FLAG_CUSTOM		0x08
-#define WQ_FLAG_DONE		0x10
-#define WQ_FLAG_PRIORITY	0x20
+#define WQ_FLAG_CUSTOM		0x04
+#define WQ_FLAG_DONE		0x08
+#define WQ_FLAG_PRIORITY	0x10
 
 /*
  * A single wait-queue entry structure:
@@ -212,8 +211,6 @@ __remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq
 int __wake_up(struct wait_queue_head *wq_head, unsigned int mode, int nr, void *key);
 void __wake_up_on_current_cpu(struct wait_queue_head *wq_head, unsigned int mode, 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);
 void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode, void *key);
 void __wake_up_locked_sync_key(struct wait_queue_head *wq_head, unsigned int mode, void *key);
 void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr);

kernel/sched/wait.c

@@ -57,13 +57,6 @@ void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry
 }
 EXPORT_SYMBOL(remove_wait_queue);
 
-/*
- * Scan threshold to break wait queue walk.
- * This allows a waker to take a break from holding the
- * wait queue lock during the wait queue walk.
- */
-#define WAITQUEUE_WALK_BREAK_CNT 64
-
 /*
  * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
  * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
@@ -78,21 +71,13 @@ EXPORT_SYMBOL(remove_wait_queue);
  * zero in this (rare) case, and we handle it by continuing to scan the queue.
  */
 static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
-			int nr_exclusive, int wake_flags, void *key,
-			wait_queue_entry_t *bookmark)
+			int nr_exclusive, int wake_flags, void *key)
 {
 	wait_queue_entry_t *curr, *next;
-	int cnt = 0;
 
 	lockdep_assert_held(&wq_head->lock);
 
-	if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) {
-		curr = list_next_entry(bookmark, entry);
-
-		list_del(&bookmark->entry);
-		bookmark->flags = 0;
-	} else
-		curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry);
+	curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry);
 
 	if (&curr->entry == &wq_head->head)
 		return nr_exclusive;
@@ -101,21 +86,11 @@ static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
 		unsigned flags = curr->flags;
 		int ret;
 
-		if (flags & WQ_FLAG_BOOKMARK)
-			continue;
-
 		ret = curr->func(curr, mode, wake_flags, key);
 		if (ret < 0)
 			break;
 		if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
 			break;
-
-		if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) &&
-				(&next->entry != &wq_head->head)) {
-			bookmark->flags = WQ_FLAG_BOOKMARK;
-			list_add_tail(&bookmark->entry, &next->entry);
-			break;
-		}
 	}
 
 	return nr_exclusive;
@@ -125,20 +100,12 @@ static int __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int m
 			int nr_exclusive, int wake_flags, void *key)
 {
 	unsigned long flags;
-	wait_queue_entry_t bookmark;
-	int remaining = nr_exclusive;
+	int remaining;
 
-	bookmark.flags = 0;
-	bookmark.private = NULL;
-	bookmark.func = NULL;
-	INIT_LIST_HEAD(&bookmark.entry);
-
-	do {
-		spin_lock_irqsave(&wq_head->lock, flags);
-		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);
+	spin_lock_irqsave(&wq_head->lock, flags);
+	remaining = __wake_up_common(wq_head, mode, nr_exclusive, wake_flags,
+			key);
+	spin_unlock_irqrestore(&wq_head->lock, flags);
 
 	return nr_exclusive - remaining;
 }
@@ -171,23 +138,16 @@ void __wake_up_on_current_cpu(struct wait_queue_head *wq_head, unsigned int mode
  */
 void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
 {
-	__wake_up_common(wq_head, mode, nr, 0, NULL, NULL);
+	__wake_up_common(wq_head, mode, nr, 0, NULL);
 }
 EXPORT_SYMBOL_GPL(__wake_up_locked);
 
 void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
 {
-	__wake_up_common(wq_head, mode, 1, 0, key, NULL);
+	__wake_up_common(wq_head, mode, 1, 0, key);
 }
 EXPORT_SYMBOL_GPL(__wake_up_locked_key);
 
-void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
-		unsigned int mode, void *key, wait_queue_entry_t *bookmark)
-{
-	__wake_up_common(wq_head, mode, 1, 0, key, bookmark);
-}
-EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark);
-
 /**
  * __wake_up_sync_key - wake up threads blocked on a waitqueue.
  * @wq_head: the waitqueue
@@ -233,7 +193,7 @@ EXPORT_SYMBOL_GPL(__wake_up_sync_key);
 void __wake_up_locked_sync_key(struct wait_queue_head *wq_head,
 			       unsigned int mode, void *key)
 {
-        __wake_up_common(wq_head, mode, 1, WF_SYNC, key, NULL);
+        __wake_up_common(wq_head, mode, 1, WF_SYNC, key);
 }
 EXPORT_SYMBOL_GPL(__wake_up_locked_sync_key);