X-Git-Url: https://git.liburcu.org/?a=blobdiff_plain;f=urcu%2Frculfqueue.h;h=b712998c07a929cfa5d49da370bd0c676c72ecdb;hb=05dd4b94f48c1717c18e0dcee88830394a5f171c;hp=f9b14fe93657343c5e1917ab77afcab4dc087a0d;hpb=453629a9317adef5b96c3d55e4dcd98db680997a;p=urcu.git

diff --git a/urcu/rculfqueue.h b/urcu/rculfqueue.h
index f9b14fe..b712998 100644
--- a/urcu/rculfqueue.h
+++ b/urcu/rculfqueue.h
@@ -1,3 +1,6 @@
+#ifndef _URCU_RCULFQUEUE_H
+#define _URCU_RCULFQUEUE_H
+
 /*
  * rculfqueue.h
  *
@@ -72,13 +75,13 @@ void rcu_lfq_enqueue(struct rcu_lfq_queue *q, struct rcu_lfq_node *node)
 	 * node before publication.
 	 */
 
-	rcu_read_lock();
 	for (;;) {
-		struct rcu_lfq_node *tail = rcu_dereference(q->tail);
-		struct rcu_lfq_node *next;
+		struct rcu_lfq_node *tail, *next;
 
+		rcu_read_lock();
+		tail = rcu_dereference(q->tail);
 		/*
-		 * Typically expect tail to be NULL.
+		 * Typically expect tail->next to be NULL.
 		 */
 		next = uatomic_cmpxchg(&tail->next, NULL, node);
 		if (next == NULL) {
@@ -97,6 +100,7 @@ void rcu_lfq_enqueue(struct rcu_lfq_queue *q, struct rcu_lfq_node *node)
 			 * further and retry.
 			 */
 			uatomic_cmpxchg(&q->tail, tail, next);
+			rcu_read_unlock();
 			continue;
 		}
 	}
@@ -107,17 +111,19 @@ void rcu_lfq_enqueue(struct rcu_lfq_queue *q, struct rcu_lfq_node *node)
  * which calls the release primitive when the reference count drops to zero. A
  * grace period must be waited before performing the actual memory reclamation
  * in the release primitive.
- * The entry lfq node returned by dequeue must no be re-used before the
- * reference count reaches zero.
+ * The entry lfq node returned by dequeue must not be modified/re-used/freed
+ * until the reference count reaches zero and a grace period has elapsed (after
+ * the refcount reached 0).
  */
 struct rcu_lfq_node *
 rcu_lfq_dequeue(struct rcu_lfq_queue *q, void (*release)(struct urcu_ref *))
 {
-	rcu_read_lock();
 	for (;;) {
-		struct rcu_lfq_node *head = rcu_dereference(q->head);
-		struct rcu_lfq_node *next = rcu_dereference(head->next);
+		struct rcu_lfq_node *head, *next;
 
+		rcu_read_lock();
+		head = rcu_dereference(q->head);
+		next = rcu_dereference(head->next);
 		if (next) {
 			if (uatomic_cmpxchg(&q->head, head, next) == head) {
 				rcu_read_unlock();
@@ -125,6 +131,7 @@ rcu_lfq_dequeue(struct rcu_lfq_queue *q, void (*release)(struct urcu_ref *))
 				return next;
 			} else {
 				/* Concurrently pushed, retry */
+				rcu_read_unlock();
 				continue;
 			}
 		} else {
@@ -134,3 +141,5 @@ rcu_lfq_dequeue(struct rcu_lfq_queue *q, void (*release)(struct urcu_ref *))
 		}
 	}
 }
+
+#endif /* _URCU_RCULFQUEUE_H */