urcu lfstack: pop needs rcu read lock

[urcu.git] / urcu / rculfstack-static.h

diff --git a/urcu/rculfstack-static.h b/urcu/rculfstack-static.h
index 49e5ef4adf905530d82577544d35ae6e1602f895..3ce24c55d2ddcf385f9e90006a016b305b557766 100644 (file)
--- a/urcu/rculfstack-static.h
+++ b/urcu/rculfstack-static.h
@@ -68,22 +68,28 @@ void _rcu_lfs_push(struct rcu_lfs_stack *s, struct rcu_lfs_node *node)
 struct rcu_lfs_node *
 _rcu_lfs_pop(struct rcu_lfs_stack *s)
 {
-       struct rcu_lfs_node *head = NULL;
-
        for (;;) {
-               struct rcu_lfs_node *old_head = head;
-               struct rcu_lfs_node *next;
+               struct rcu_lfs_node *head;
 
-               if (head)
-                       next = head->next;
-               else
-                       next = NULL;
+               rcu_read_lock();
+               head = rcu_dereference(s->head);
+               if (head) {
+                       struct rcu_lfs_node *next = rcu_dereference(head->next);
 
-               head = uatomic_cmpxchg(&s->head, old_head, next);
-               if (old_head == head)
-                       break;
+                       if (uatomic_cmpxchg(&s->head, head, next) == head) {
+                               rcu_read_unlock();
+                               return head;
+                       } else {
+                               /* Concurrent modification. Retry. */
+                               rcu_read_unlock();
+                               continue;
+                       }
+               } else {
+                       /* Empty stack */
+                       rcu_read_unlock();
+                       return NULL;
+               }
        }
-       return head;
 }
 
 #ifdef __cplusplus