[PATCH 07/45] FS-Cache: Provide an add_wait_queue_tail() function[ver #41]

[David Howells]

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@xxxxxxxxxx>
---

 include/linux/wait.h |    1 +
 kernel/wait.c        |   18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 0 deletions(-)


diff --git a/include/linux/wait.h b/include/linux/wait.h
index ef609f8..f35de07 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -109,6 +109,7 @@ static inline int waitqueue_active(wait_queue_head_t *q)
 }
 
 extern void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait);
+extern void add_wait_queue_tail(wait_queue_head_t *q, wait_queue_t *wait);
 extern void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait);
 extern void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait);
 
diff --git a/kernel/wait.c b/kernel/wait.c
index cd87131..e2475af 100644
--- a/kernel/wait.c
+++ b/kernel/wait.c
@@ -29,6 +29,24 @@ void 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 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 add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
 {
 	unsigned long flags;

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