RDS: Remove unused XLIST_PTR_TAIL and xlist_protect()

Not used.
Signed-off-by: Andy Grover <andy.grover@oracle.com>

net/rds/xlist.h

@@ -10,13 +10,18 @@ struct xlist_head {
 	struct xlist_head *next;
 };
 
-/*
- * XLIST_PTR_TAIL can be used to prevent double insertion.  See
- * xlist_protect()
- */
-#define XLIST_PTR_TAIL ((struct xlist_head *)0x1)
+static inline void INIT_XLIST_HEAD(struct xlist_head *list)
+{
+	list->next = NULL;
+}
 
-static inline void xlist_add(struct xlist_head *new, struct xlist_head *tail, struct xlist_head *head)
+static inline int xlist_empty(struct xlist_head *head)
+{
+	return head->next == NULL;
+}
+
+static inline void xlist_add(struct xlist_head *new, struct xlist_head *tail,
+			     struct xlist_head *head)
 {
 	struct xlist_head *cur;
 	struct xlist_head *check;
@@ -30,26 +35,6 @@ static inline void xlist_add(struct xlist_head *new, struct xlist_head *tail, st
 	}
 }
 
-/*
- * To avoid duplicate insertion by two CPUs of the same xlist item
- * you can call xlist_protect.  It will stuff XLIST_PTR_TAIL
- * into the entry->next pointer with xchg, and only return 1
- * if there was a NULL there before.
- *
- * if xlist_protect returns zero, someone else is busy working
- * on this entry.  Getting a NULL into the entry in a race
- * free manner is the caller's job.
- */
-static inline int xlist_protect(struct xlist_head *entry)
-{
-	struct xlist_head *val;
-
-	val = xchg(&entry->next, XLIST_PTR_TAIL);
-	if (val == NULL)
-		return 1;
-	return 0;
-}
-
 static inline struct xlist_head *xlist_del_head(struct xlist_head *head)
 {
 	struct xlist_head *cur;
@@ -61,11 +46,6 @@ static inline struct xlist_head *xlist_del_head(struct xlist_head *head)
 		if (!cur)
 			goto out;
 
-		if (cur == XLIST_PTR_TAIL) {
-			cur = NULL;
-			goto out;
-		}
-
 		next = cur->next;
 		check = cmpxchg(&head->next, cur, next);
 		if (check == cur)
@@ -80,7 +60,7 @@ static inline struct xlist_head *xlist_del_head_fast(struct xlist_head *head)
 	struct xlist_head *cur;
 
 	cur = head->next;
-	if (!cur || cur == XLIST_PTR_TAIL)
+	if (!cur)
 		return NULL;
 
 	head->next = cur->next;
@@ -97,14 +77,4 @@ static inline void xlist_splice(struct xlist_head *list,
 	head->next = cur;
 }
 
-static inline void INIT_XLIST_HEAD(struct xlist_head *list)
-{
-	list->next = NULL;
-}
-
-static inline int xlist_empty(struct xlist_head *head)
-{
-	return head->next == NULL || head->next == XLIST_PTR_TAIL;
-}
-
 #endif