list: add "list_del_init_careful()" to go with "list_empty_careful()"

That gives us ordering guarantees around the pair.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 19 insertions, 1 deletions

diff --git a/include/linux/list.h b/include/linux/list.h
index aff44d34f4e4..0d0d17a10d25 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -283,6 +283,24 @@ static inline int list_empty(const struct list_head *head)
 }
 
 /**
+ * list_del_init_careful - deletes entry from list and reinitialize it.
+ * @entry: the element to delete from the list.
+ *
+ * This is the same as list_del_init(), except designed to be used
+ * together with list_empty_careful() in a way to guarantee ordering
+ * of other memory operations.
+ *
+ * Any memory operations done before a list_del_init_careful() are
+ * guaranteed to be visible after a list_empty_careful() test.
+ */
+static inline void list_del_init_careful(struct list_head *entry)
+{
+	__list_del_entry(entry);
+	entry->prev = entry;
+	smp_store_release(&entry->next, entry);
+}
+
+/**
  * list_empty_careful - tests whether a list is empty and not being modified
  * @head: the list to test
  *
@@ -297,7 +315,7 @@ static inline int list_empty(const struct list_head *head)
  */
 static inline int list_empty_careful(const struct list_head *head)
 {
-	struct list_head *next = head->next;
+	struct list_head *next = smp_load_acquire(&head->next);
 	return (next == head) && (next == head->prev);
 }