llist: Return whether list is empty before adding in llist_add()

Extend the llist_add*() functions to return a success indicator, this
allows us in the scheduler code to send an IPI if the queue was empty.

( There's no effect on existing users, because the list_add_xxx() functions
  are inline, thus this will be optimized out by the compiler if not used
  by callers. )

Signed-off-by: Huang Ying <ying.huang@intel.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1315461646-1379-5-git-send-email-ying.huang@intel.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 5 insertions, 1 deletions

diff --git a/lib/llist.c b/lib/llist.c
index 6c69f1d14c4b..878985c4d19d 100644
--- a/lib/llist.c
+++ b/lib/llist.c
@@ -34,8 +34,10 @@
  * @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.
  */
-void llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
+bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
                      struct llist_head *head)
 {
         struct llist_node *entry, *old_entry;
@@ -49,6 +51,8 @@ void llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
                         break;
                 cpu_relax();
         }
+
+        return old_entry == NULL;
 }
 EXPORT_SYMBOL_GPL(llist_add_batch);