Provide an add_wait_queue_tail() function to add a waiter to the back of a
wait queue instead of the front.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 include/linux/wait.h |    2 ++
 kernel/wait.c        |   18 ++++++++++++++++++
 2 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index 0e68628..f1038d0 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -118,6 +118,8 @@ static inline int waitqueue_active(wait_queue_head_t *q)
 #define is_sync_wait(wait)	(!(wait) || ((wait)->private))
 
 extern void FASTCALL(add_wait_queue(wait_queue_head_t *q, wait_queue_t * wait));
+extern void FASTCALL(add_wait_queue_tail(wait_queue_head_t *q,
+					 wait_queue_t *wait));
 extern void FASTCALL(add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t * wait));
 extern void FASTCALL(remove_wait_queue(wait_queue_head_t *q, wait_queue_t * wait));
 
diff --git a/kernel/wait.c b/kernel/wait.c
index 444ddbf..7acc9cc 100644
--- a/kernel/wait.c
+++ b/kernel/wait.c
@@ -29,6 +29,24 @@ void fastcall add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
 }
 EXPORT_SYMBOL(add_wait_queue);
 
+/**
+ * add_wait_queue_tail - Add a waiter to the back of a waitqueue
+ * @q: the wait queue to append the waiter to
+ * @wait: the waiter to be queued
+ *
+ * Add a waiter to the back of a waitqueue so that it gets woken up last.
+ */
+void fastcall add_wait_queue_tail(wait_queue_head_t *q, wait_queue_t *wait)
+{
+	unsigned long flags;
+
+	wait->flags &= ~WQ_FLAG_EXCLUSIVE;
+	spin_lock_irqsave(&q->lock, flags);
+	__add_wait_queue_tail(q, wait);
+	spin_unlock_irqrestore(&q->lock, flags);
+}
+EXPORT_SYMBOL(add_wait_queue_tail);
+
 void fastcall add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
 {
 	unsigned long flags;

--
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