mmu-notifiers: add list_del_init_rcu()

Introduce list_del_init_rcu() and document it.

Signed-off-by: Andrea Arcangeli <[email protected]>
Acked-by: Linus Torvalds <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Jack Steiner <[email protected]>
Cc: Robin Holt <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Kanoj Sarcar <[email protected]>
Cc: Roland Dreier <[email protected]>
Cc: Steve Wise <[email protected]>
Cc: Avi Kivity <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: Anthony Liguori <[email protected]>
Cc: Chris Wright <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Izik Eidus <[email protected]>
Cc: Anthony Liguori <[email protected]>
Cc: Rik van Riel <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 28 insertions, 0 deletions

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index b0f39be08b6c..eb4443c7e05b 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -98,6 +98,34 @@ static inline void list_del_rcu(struct list_head *entry)
 }
 
 /**
+ * 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;
+	}
+}
+
+/**
  * list_replace_rcu - replace old entry by new one
  * @old : the element to be replaced
  * @new : the new element to insert