llist: Add nonatomic __llist_add() and __llist_dell_all()

We'll use these in the new, lockless kretprobes code.

Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Signed-off-by: Masami Hiramatsu <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>
Link: https://lore.kernel.org/r/159870619318.1229682.13027387548510028721.stgit@devnote2

drivers/gpu/drm/i915/i915_request.c

···
 	} while (i915_request_retire(tmp) && tmp != rq);
 }
 
-static void __llist_add(struct llist_node *node, struct llist_head *head)
-{
-	node->next = head->first;
-	head->first = node;
-}
-
 static struct i915_request * const *
 __engine_active(struct intel_engine_cs *engine)
 {

include/linux/llist.h

···
 extern bool llist_add_batch(struct llist_node *new_first,
 			    struct llist_node *new_last,
 			    struct llist_head *head);
+
+static inline bool __llist_add_batch(struct llist_node *new_first,
+				     struct llist_node *new_last,
+				     struct llist_head *head)
+{
+	new_last->next = head->first;
+	head->first = new_first;
+	return new_last->next == NULL;
+}
+
 /**
  * llist_add - add a new entry
  * @new:	new entry to be added
···
 static inline bool llist_add(struct llist_node *new, struct llist_head *head)
 {
 	return llist_add_batch(new, new, head);
+}
+
+static inline bool __llist_add(struct llist_node *new, struct llist_head *head)
+{
+	return __llist_add_batch(new, new, head);
 }
 
 /**
···
 static inline struct llist_node *llist_del_all(struct llist_head *head)
 {
 	return xchg(&head->first, NULL);
+}
+
+static inline struct llist_node *__llist_del_all(struct llist_head *head)
+{
+	struct llist_node *first = head->first;
+
+	head->first = NULL;
+	return first;
 }
 
 extern struct llist_node *llist_del_first(struct llist_head *head);