sched, wait: Use wrapper functions

epoll should not touch flags in wait_queue_t. This patch introduces a new
function __add_wait_queue_exclusive(), for the users, who use wait queue as a
LIFO queue.

__add_wait_queue_tail_exclusive() is introduced too instead of
add_wait_queue_exclusive_locked(). remove_wait_queue_locked() is removed, as
it is a duplicate of __remove_wait_queue(), disliked by users, and with less
users.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: <containers@lists.linux-foundation.org>
LKML-Reference: <1273214006-2979-1-git-send-email-xiaosuo@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

fs/eventpoll.c

@@ -1140,8 +1140,7 @@ retry:
 		 * ep_poll_callback() when events will become available.
 		 */
 		init_waitqueue_entry(&wait, current);
-		wait.flags |= WQ_FLAG_EXCLUSIVE;
+		__add_wait_queue_exclusive(&ep->wq, &wait);
-		__add_wait_queue(&ep->wq, &wait);
 
 		for (;;) {
 			/*

include/linux/wait.h

@@ -127,12 +127,26 @@ static inline void __add_wait_queue(wait_queue_head_t *head, wait_queue_t *new)
 /*
  * Used for wake-one threads:
  */
+static inline void __add_wait_queue_exclusive(wait_queue_head_t *q,
+					      wait_queue_t *wait)
+{
+	wait->flags |= WQ_FLAG_EXCLUSIVE;
+	__add_wait_queue(q, wait);
+}
+
 static inline void __add_wait_queue_tail(wait_queue_head_t *head,
-						wait_queue_t *new)
+					 wait_queue_t *new)
 {
 	list_add_tail(&new->task_list, &head->task_list);
 }
 
+static inline void __add_wait_queue_tail_exclusive(wait_queue_head_t *q,
+					      wait_queue_t *wait)
+{
+	wait->flags |= WQ_FLAG_EXCLUSIVE;
+	__add_wait_queue_tail(q, wait);
+}
+
 static inline void __remove_wait_queue(wait_queue_head_t *head,
 							wait_queue_t *old)
 {
@@ -403,25 +417,6 @@ do {									\
 	__ret;								\
 })
 
-/*
- * Must be called with the spinlock in the wait_queue_head_t held.
- */
-static inline void add_wait_queue_exclusive_locked(wait_queue_head_t *q,
-						   wait_queue_t * wait)
-{
-	wait->flags |= WQ_FLAG_EXCLUSIVE;
-	__add_wait_queue_tail(q,  wait);
-}
-
-/*
- * Must be called with the spinlock in the wait_queue_head_t held.
- */
-static inline void remove_wait_queue_locked(wait_queue_head_t *q,
-					    wait_queue_t * wait)
-{
-	__remove_wait_queue(q,  wait);
-}
-
 /*
  * These are the old interfaces to sleep waiting for an event.
  * They are racy.  DO NOT use them, use the wait_event* interfaces above.

kernel/cgroup.c

@@ -3010,7 +3010,7 @@ static int cgroup_event_wake(wait_queue_t *wait, unsigned mode,
 	unsigned long flags = (unsigned long)key;
 
 	if (flags & POLLHUP) {
-		remove_wait_queue_locked(event->wqh, &event->wait);
+		__remove_wait_queue(event->wqh, &event->wait);
 		spin_lock(&cgrp->event_list_lock);
 		list_del(&event->list);
 		spin_unlock(&cgrp->event_list_lock);

kernel/sched.c

@@ -3983,8 +3983,7 @@ do_wait_for_common(struct completion *x, long timeout, int state)
 	if (!x->done) {
 		DECLARE_WAITQUEUE(wait, current);
 
-		wait.flags |= WQ_FLAG_EXCLUSIVE;
+		__add_wait_queue_tail_exclusive(&x->wait, &wait);
-		__add_wait_queue_tail(&x->wait, &wait);
 		do {
 			if (signal_pending_state(state, current)) {
 				timeout = -ERESTARTSYS;