[PATCH -mm -v2 4/5] llist, Return whether list is empty before adding in llist_add

[Huang Ying <ying.huang@intel.com>]

This is needed by irq_work.  And because list_add_xxx functions are
inline, this can be optimized out if not needed by callers.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 include/linux/llist.h |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- a/include/linux/llist.h
+++ b/include/linux/llist.h
@@ -148,8 +148,10 @@ static inline bool llist_empty(const str
  * llist_add - add a new entry
  * @new:	new entry to be added
  * @head:	the head for your lock-less list
+ *
+ * Return whether list is empty before adding.
  */
-static inline void llist_add(struct llist_node *new, struct llist_head *head)
+static inline bool llist_add(struct llist_node *new, struct llist_head *head)
 {
 	struct llist_node *entry, *old_entry;
 
@@ -164,6 +166,8 @@ static inline void llist_add(struct llis
 			break;
 		cpu_relax();
 	}
+
+	return old_entry == NULL;
 }
 
 /**
@@ -171,8 +175,10 @@ static inline void llist_add(struct llis
  * @new_first:	first entry in batch to be added
  * @new_last:	last entry in batch to be added
  * @head:	the head for your lock-less list
+ *
+ * Return whether list is empty before adding.
  */
-static inline void llist_add_batch(struct llist_node *new_first,
+static inline bool llist_add_batch(struct llist_node *new_first,
 				   struct llist_node *new_last,
 				   struct llist_head *head)
 {
@@ -189,6 +195,8 @@ static inline void llist_add_batch(struc
 			break;
 		cpu_relax();
 	}
+
+	return old_entry == NULL;
 }
 
 /**