rcu: Introduce hlist_nulls variant of hlist

[pandora-kernel.git] / include / linux / rculist_nulls.h

diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h
new file mode 100644 (file)
index 0000000..f9ddd03
--- /dev/null
+++ b/include/linux/rculist_nulls.h
@@ -0,0 +1,110 @@
+#ifndef _LINUX_RCULIST_NULLS_H
+#define _LINUX_RCULIST_NULLS_H
+
+#ifdef __KERNEL__
+
+/*
+ * RCU-protected list version
+ */
+#include <linux/list_nulls.h>
+#include <linux/rcupdate.h>
+
+/**
+ * hlist_nulls_del_init_rcu - deletes entry from hash list with re-initialization
+ * @n: the element to delete from the hash list.
+ *
+ * Note: hlist_nulls_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_nulls_add_head_rcu() or
+ * hlist_nulls_del_rcu(), running on this same list.  However, it is
+ * perfectly legal to run concurrently with the _rcu list-traversal
+ * primitives, such as hlist_nulls_for_each_entry_rcu().
+ */
+static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)
+{
+       if (!hlist_nulls_unhashed(n)) {
+               __hlist_nulls_del(n);
+               n->pprev = NULL;
+       }
+}
+
+/**
+ * hlist_nulls_del_rcu - deletes entry from hash list without re-initialization
+ * @n: the element to delete from the hash list.
+ *
+ * Note: hlist_nulls_unhashed() on entry does not return true after this,
+ * the entry is in an undefined state. It is useful for RCU based
+ * lockfree traversal.
+ *
+ * In particular, it means that we can not poison the forward
+ * pointers that may still be used for walking the hash list.
+ *
+ * The caller must take whatever precautions are necessary
+ * (such as holding appropriate locks) to avoid racing
+ * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
+ * or hlist_nulls_del_rcu(), running on this same list.
+ * However, it is perfectly legal to run concurrently with
+ * the _rcu list-traversal primitives, such as
+ * hlist_nulls_for_each_entry().
+ */
+static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n)
+{
+       __hlist_nulls_del(n);
+       n->pprev = LIST_POISON2;
+}
+
+/**
+ * hlist_nulls_add_head_rcu
+ * @n: the element to add to the hash list.
+ * @h: the list to add to.
+ *
+ * Description:
+ * Adds the specified element to the specified hlist_nulls,
+ * while permitting racing traversals.
+ *
+ * The caller must take whatever precautions are necessary
+ * (such as holding appropriate locks) to avoid racing
+ * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
+ * or hlist_nulls_del_rcu(), running on this same list.
+ * However, it is perfectly legal to run concurrently with
+ * the _rcu list-traversal primitives, such as
+ * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
+ * problems on Alpha CPUs.  Regardless of the type of CPU, the
+ * list-traversal primitive must be guarded by rcu_read_lock().
+ */
+static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
+                                       struct hlist_nulls_head *h)
+{
+       struct hlist_nulls_node *first = h->first;
+
+       n->next = first;
+       n->pprev = &h->first;
+       rcu_assign_pointer(h->first, n);
+       if (!is_a_nulls(first))
+               first->pprev = &n->next;
+}
+/**
+ * hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type
+ * @tpos:      the type * to use as a loop cursor.
+ * @pos:       the &struct hlist_nulls_node to use as a loop cursor.
+ * @head:      the head for your list.
+ * @member:    the name of the hlist_nulls_node within the struct.
+ *
+ */
+#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \
+       for (pos = rcu_dereference((head)->first);                       \
+               (!is_a_nulls(pos)) &&                   \
+               ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
+               pos = rcu_dereference(pos->next))
+
+#endif
+#endif