[PATCH 1 of 3] list_del_init_rcu

Andrea Arcangeli
2008-06-26T00:26:57Z

Introduces list_del_init_rcu and documents it (fixes a comment for
list_del_rcu too).

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff -r 98f755616212 -r 5e8c41d283cc include/linux/list.h
--- a/include/linux/list.h Tue Jun 24 11:23:35 2008 -0700
+++ b/include/linux/list.h Wed Jun 25 03:34:11 2008 +0200
@@ -747,7 +747,7 @@ static inline void hlist_del(struct hlis
* or hlist_del_rcu(), running on this same list.
* However, it is perfectly legal to run concurrently with
* the _rcu list-traversal primitives, such as
- * hlist_for_each_entry().
+ * hlist_for_each_entry_rcu().
*/
static inline void hlist_del_rcu(struct hlist_node *n)
{
@@ -760,6 +760,34 @@ static inline void hlist_del_init(struct
if (!hlist_unhashed(n)) {
__hlist_del(n);
INIT_HLIST_NODE(n);
+ }
+}
+
+/**
+ * hlist_del_init_rcu - deletes entry from hash list with re-initialization
+ * @n: the element to delete from the hash list.
+ *
+ * Note: list_unhashed() on the node return true after this. It is
+ * useful for RCU based read lockfree traversal if the writer side
+ * must know if the list entry is still hashed or already unhashed.
+ *
+ * In particular, it means that we can not poison the forward pointers
+ * that may still be used for walking the hash list and we can only
+ * zero the pprev pointer so list_unhashed() will return true after
+ * this.
+ *
+ * The caller must take whatever precautions are necessary (such as
+ * holding appropriate locks) to avoid racing with another
+ * list-mutation primitive, such as hlist_add_head_rcu() or
+ * hlist_del_rcu(), running on this same list. However, it is
+ * perfectly legal to run concurrently with the _rcu list-traversal
+ * primitives, such as hlist_for_each_entry_rcu().
+ */
+static inline void hlist_del_init_rcu(struct hlist_node *n)
+{
+ if (!hlist_unhashed(n)) {
+ __hlist_del(n);
+ n->pprev = NULL;
}
}