2 files changed, 71 insertions, 28 deletions

diff --git a/include/linux/klist.h b/include/linux/klist.h
index 06c338ef7f1b..8ea98db223e5 100644
--- a/include/linux/klist.h
+++ b/include/linux/klist.h
@@ -38,7 +38,7 @@ extern void klist_init(struct klist *k, void (*get)(struct klist_node *),
                        void (*put)(struct klist_node *));
 
 struct klist_node {
-        struct klist            *n_klist;
+        void                    *n_klist;       /* never access directly */
         struct list_head        n_node;
         struct kref             n_ref;
         struct completion       n_removed;
@@ -57,7 +57,6 @@ extern int klist_node_attached(struct klist_node *n);
 
 struct klist_iter {
         struct klist            *i_klist;
-        struct list_head        *i_head;
         struct klist_node       *i_cur;
 };
 
diff --git a/lib/klist.c b/lib/klist.c
index cca37f96faa2..bbdd3015c2c7 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);