1 files changed, 70 insertions, 26 deletions

diff --git a/lib/klist.c b/lib/klist.c
index cca37f9..bbdd301 100644
--- a/lib/klist.c
+++ b/lib/klist.c
@@ -37,6 +37,37 @@
 #include <linux/klist.h>
 #include <linux/module.h>
 
+/*
+ * Use the lowest bit of n_klist to mark deleted nodes and exclude
+ * dead ones from iteration.
+ */
+#define KNODE_DEAD		1LU
+#define KNODE_KLIST_MASK	~KNODE_DEAD
+
+static struct klist *knode_klist(struct klist_node *knode)
+{
+	return (struct klist *)
+		((unsigned long)knode->n_klist & KNODE_KLIST_MASK);
+}
+
+static bool knode_dead(struct klist_node *knode)
+{
+	return (unsigned long)knode->n_klist & KNODE_DEAD;
+}
+
+static void knode_set_klist(struct klist_node *knode, struct klist *klist)
+{
+	knode->n_klist = klist;
+	/* no knode deserves to start its life dead */
+	WARN_ON(knode_dead(knode));
+}
+
+static void knode_kill(struct klist_node *knode)
+{
+	/* and no knode should die twice ever either, see we're very humane */
+	WARN_ON(knode_dead(knode));
+	*(unsigned long *)&knode->n_klist |= KNODE_DEAD;
+}
 
 /**
  * klist_init - Initialize a klist structure.
@@ -79,7 +110,7 @@ static void klist_node_init(struct klist *k, struct klist_node *n)
 	INIT_LIST_HEAD(&n->n_node);
 	init_completion(&n->n_removed);
 	kref_init(&n->n_ref);
-	n->n_klist = k;
+	knode_set_klist(n, k);
 	if (k->get)
 		k->get(n);
 }
@@ -115,7 +146,7 @@ EXPORT_SYMBOL_GPL(klist_add_tail);
  */
 void klist_add_after(struct klist_node *n, struct klist_node *pos)
 {
-	struct klist *k = pos->n_klist;
+	struct klist *k = knode_klist(pos);
 
 	klist_node_init(k, n);
 	spin_lock(&k->k_lock);
@@ -131,7 +162,7 @@ EXPORT_SYMBOL_GPL(klist_add_after);
  */
 void klist_add_before(struct klist_node *n, struct klist_node *pos)
 {
-	struct klist *k = pos->n_klist;
+	struct klist *k = knode_klist(pos);
 
 	klist_node_init(k, n);
 	spin_lock(&k->k_lock);
@@ -144,9 +175,10 @@ static void klist_release(struct kref *kref)
 {
 	struct klist_node *n = container_of(kref, struct klist_node, n_ref);
 
+	WARN_ON(!knode_dead(n));
 	list_del(&n->n_node);
 	complete(&n->n_removed);
-	n->n_klist = NULL;
+	knode_set_klist(n, NULL);
 }
 
 static int klist_dec_and_del(struct klist_node *n)
@@ -154,22 +186,29 @@ static int klist_dec_and_del(struct klist_node *n)
 	return kref_put(&n->n_ref, klist_release);
 }
 
-/**
- * klist_del - Decrement the reference count of node and try to remove.
- * @n: node we're deleting.
- */
-void klist_del(struct klist_node *n)
+static void klist_put(struct klist_node *n, bool kill)
 {
-	struct klist *k = n->n_klist;
+	struct klist *k = knode_klist(n);
 	void (*put)(struct klist_node *) = k->put;
 
 	spin_lock(&k->k_lock);
+	if (kill)
+		knode_kill(n);
 	if (!klist_dec_and_del(n))
 		put = NULL;
 	spin_unlock(&k->k_lock);
 	if (put)
 		put(n);
 }
+
+/**
+ * klist_del - Decrement the reference count of node and try to remove.
+ * @n: node we're deleting.
+ */
+void klist_del(struct klist_node *n)
+{
+	klist_put(n, true);
+}
 EXPORT_SYMBOL_GPL(klist_del);
 
 /**
@@ -206,7 +245,6 @@ void klist_iter_init_node(struct klist *k, struct klist_iter *i,
 			  struct klist_node *n)
 {
 	i->i_klist = k;
-	i->i_head = &k->k_list;
 	i->i_cur = n;
 	if (n)
 		kref_get(&n->n_ref);
@@ -237,7 +275,7 @@ EXPORT_SYMBOL_GPL(klist_iter_init);
 void klist_iter_exit(struct klist_iter *i)
 {
 	if (i->i_cur) {
-		klist_del(i->i_cur);
+		klist_put(i->i_cur, false);
 		i->i_cur = NULL;
 	}
 }
@@ -258,27 +296,33 @@ static struct klist_node *to_klist_node(struct list_head *n)
  */
 struct klist_node *klist_next(struct klist_iter *i)
 {
-	struct list_head *next;
-	struct klist_node *lnode = i->i_cur;
-	struct klist_node *knode = NULL;
 	void (*put)(struct klist_node *) = i->i_klist->put;
+	struct klist_node *last = i->i_cur;
+	struct klist_node *next;
 
 	spin_lock(&i->i_klist->k_lock);
-	if (lnode) {
-		next = lnode->n_node.next;
-		if (!klist_dec_and_del(lnode))
+
+	if (last) {
+		next = to_klist_node(last->n_node.next);
+		if (!klist_dec_and_del(last))
 			put = NULL;
 	} else
-		next = i->i_head->next;
+		next = to_klist_node(i->i_klist->k_list.next);
 
-	if (next != i->i_head) {
-		knode = to_klist_node(next);
-		kref_get(&knode->n_ref);
+	i->i_cur = NULL;
+	while (next != to_klist_node(&i->i_klist->k_list)) {
+		if (likely(!knode_dead(next))) {
+			kref_get(&next->n_ref);
+			i->i_cur = next;
+			break;
+		}
+		next = to_klist_node(next->n_node.next);
 	}
-	i->i_cur = knode;
+
 	spin_unlock(&i->i_klist->k_lock);
-	if (put && lnode)
-		put(lnode);
-	return knode;
+
+	if (put && last)
+		put(last);
+	return i->i_cur;
 }
 EXPORT_SYMBOL_GPL(klist_next);