RCU lock-free queue: don't hold RCU read lock across retry

[urcu.git] / urcu / rculfqueue.h

diff --git a/urcu/rculfqueue.h b/urcu/rculfqueue.h
index f9b14fe93657343c5e1917ab77afcab4dc087a0d..09e5d41ea0db7b7f40032419b070ed55daecdfdd 100644 (file)
--- a/urcu/rculfqueue.h
+++ b/urcu/rculfqueue.h
@@ -72,13 +72,13 @@ 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 +97,7 @@ 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 +108,18 @@ 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
+ * The entry lfq node returned by dequeue must not be re-used before the
  * reference count reaches zero.
  */
 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 +127,7 @@ rcu_lfq_dequeue(struct rcu_lfq_queue *q, void (*release)(struct urcu_ref *))
                                return next;
                        } else {
                                /* Concurrently pushed, retry */
+                               rcu_read_unlock();
                                continue;
                        }
                } else {