1 files changed, 189 insertions, 0 deletions
diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h
new file mode 100644
index 000000000..d8afdb878
--- /dev/null
+++ b/include/linux/rculist_nulls.h
@@ -0,0 +1,189 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#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);
+		WRITE_ONCE(n->pprev, NULL);
+	}
+}
+
+/**
+ * hlist_nulls_first_rcu - returns the first element of the hash list.
+ * @head: the head of the list.
+ */
+#define hlist_nulls_first_rcu(head) \
+	(*((struct hlist_nulls_node __rcu __force **)&(head)->first))
+
+/**
+ * hlist_nulls_next_rcu - returns the element of the list after @node.
+ * @node: element of the list.
+ */
+#define hlist_nulls_next_rcu(node) \
+	(*((struct hlist_nulls_node __rcu __force **)&(node)->next))
+
+/**
+ * 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);
+	WRITE_ONCE(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;
+	WRITE_ONCE(n->pprev, &h->first);
+	rcu_assign_pointer(hlist_nulls_first_rcu(h), n);
+	if (!is_a_nulls(first))
+		WRITE_ONCE(first->pprev, &n->next);
+}
+
+/**
+ * hlist_nulls_add_tail_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_tail_rcu(struct hlist_nulls_node *n,
+					    struct hlist_nulls_head *h)
+{
+	struct hlist_nulls_node *i, *last = NULL;
+
+	/* Note: write side code, so rcu accessors are not needed. */
+	for (i = h->first; !is_a_nulls(i); i = i->next)
+		last = i;
+
+	if (last) {
+		n->next = last->next;
+		n->pprev = &last->next;
+		rcu_assign_pointer(hlist_next_rcu(last), n);
+	} else {
+		hlist_nulls_add_head_rcu(n, h);
+	}
+}
+
+/* after that hlist_nulls_del will work */
+static inline void hlist_nulls_add_fake(struct hlist_nulls_node *n)
+{
+	n->pprev = &n->next;
+	n->next = (struct hlist_nulls_node *)NULLS_MARKER(NULL);
+}
+
+/**
+ * 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 of the list.
+ * @member:	the name of the hlist_nulls_node within the struct.
+ *
+ * The barrier() is needed to make sure compiler doesn't cache first element [1],
+ * as this loop can be restarted [2]
+ * [1] Documentation/memory-barriers.txt around line 1533
+ * [2] Documentation/RCU/rculist_nulls.rst around line 146
+ */
+#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member)			\
+	for (({barrier();}),							\
+	     pos = rcu_dereference_raw(hlist_nulls_first_rcu(head));		\
+		(!is_a_nulls(pos)) &&						\
+		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
+		pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)))
+
+/**
+ * hlist_nulls_for_each_entry_safe -
+ *   iterate over list of given type safe against removal of list entry
+ * @tpos:	the type * to use as a loop cursor.
+ * @pos:	the &struct hlist_nulls_node to use as a loop cursor.
+ * @head:	the head of the list.
+ * @member:	the name of the hlist_nulls_node within the struct.
+ */
+#define hlist_nulls_for_each_entry_safe(tpos, pos, head, member)		\
+	for (({barrier();}),							\
+	     pos = rcu_dereference_raw(hlist_nulls_first_rcu(head));		\
+		(!is_a_nulls(pos)) &&						\
+		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member);	\
+		   pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)); 1; });)
+#endif
+#endif