CDS API: removal of rcu_read lock/unlock dep, removal of call_rcu argument from init

[urcu.git] / urcu / static / rculfqueue.h

diff --git a/urcu/static/rculfqueue.h b/urcu/static/rculfqueue.h
index 6045c184d22b2b9af8ea0c03bb33a1f026d24be0..99335c41ec41d33078279e2f843431111cf307e8 100644 (file)
--- a/urcu/static/rculfqueue.h
+++ b/urcu/static/rculfqueue.h
@@ -59,12 +59,6 @@ struct cds_lfq_node_rcu_dummy {
  * grace period.
  */
 
-static inline
-int is_dummy(struct cds_lfq_queue_rcu *q, struct cds_lfq_node_rcu *node)
-{
-       return node == CMM_LOAD_SHARED(q->dummy);
-}
-
 static inline
 struct cds_lfq_node_rcu *make_dummy(struct cds_lfq_queue_rcu *q,
                                    struct cds_lfq_node_rcu *next)
@@ -74,12 +68,13 @@ struct cds_lfq_node_rcu *make_dummy(struct cds_lfq_queue_rcu *q,
        dummy = malloc(sizeof(struct cds_lfq_node_rcu_dummy));
        assert(dummy);
        dummy->parent.next = next;
+       dummy->parent.dummy = 1;
        dummy->q = q;
        return &dummy->parent;
 }
 
 static inline
-void free_dummy(struct rcu_head *head)
+void free_dummy_cb(struct rcu_head *head)
 {
        struct cds_lfq_node_rcu_dummy *dummy =
                caa_container_of(head, struct cds_lfq_node_rcu_dummy, head);
@@ -91,25 +86,33 @@ void rcu_free_dummy(struct cds_lfq_node_rcu *node)
 {
        struct cds_lfq_node_rcu_dummy *dummy;
 
+       assert(node->dummy);
+       dummy = caa_container_of(node, struct cds_lfq_node_rcu_dummy, parent);
+       call_rcu(&dummy->head, free_dummy_cb);
+}
+
+static inline
+void free_dummy(struct cds_lfq_node_rcu *node)
+{
+       struct cds_lfq_node_rcu_dummy *dummy;
+
+       assert(node->dummy);
        dummy = caa_container_of(node, struct cds_lfq_node_rcu_dummy, parent);
-       dummy->q->queue_call_rcu(&dummy->head, free_dummy);
+       free(dummy);
 }
 
 static inline
 void _cds_lfq_node_init_rcu(struct cds_lfq_node_rcu *node)
 {
        node->next = NULL;
+       node->dummy = 0;
 }
 
 static inline
-void _cds_lfq_init_rcu(struct cds_lfq_queue_rcu *q,
-                      void queue_call_rcu(struct rcu_head *head,
-                               void (*func)(struct rcu_head *head)))
+void _cds_lfq_init_rcu(struct cds_lfq_queue_rcu *q)
 {
        q->tail = make_dummy(q, NULL);
-       q->dummy = q->tail;
        q->head = q->tail;
-       q->queue_call_rcu = queue_call_rcu;
 }
 
 /*
@@ -123,14 +126,14 @@ int _cds_lfq_destroy_rcu(struct cds_lfq_queue_rcu *q)
        struct cds_lfq_node_rcu *head;
 
        head = rcu_dereference(q->head);
-       if (!(is_dummy(q, head) && head->next == NULL))
+       if (!(head->dummy && head->next == NULL))
                return -EPERM;  /* not empty */
-       rcu_free_dummy(head);
+       free_dummy(head);
        return 0;
 }
 
 /*
- * Should be called under rcu read lock critical section.
+ * Acts as a RCU reader.
  */
 static inline
 void _cds_lfq_enqueue_rcu(struct cds_lfq_queue_rcu *q,
@@ -144,6 +147,7 @@ void _cds_lfq_enqueue_rcu(struct cds_lfq_queue_rcu *q,
        for (;;) {
                struct cds_lfq_node_rcu *tail, *next;
 
+               rcu_read_lock();
                tail = rcu_dereference(q->tail);
                next = uatomic_cmpxchg(&tail->next, NULL, node);
                if (next == NULL) {
@@ -153,6 +157,7 @@ void _cds_lfq_enqueue_rcu(struct cds_lfq_queue_rcu *q,
                         * enqueue might beat us to it, that's fine).
                         */
                        (void) uatomic_cmpxchg(&q->tail, tail, node);
+                       rcu_read_unlock();
                        return;
                } else {
                        /*
@@ -160,13 +165,24 @@ void _cds_lfq_enqueue_rcu(struct cds_lfq_queue_rcu *q,
                         * Help moving tail further and retry.
                         */
                        (void) uatomic_cmpxchg(&q->tail, tail, next);
+                       rcu_read_unlock();
                        continue;
                }
        }
 }
 
+static inline
+void enqueue_dummy(struct cds_lfq_queue_rcu *q)
+{
+       struct cds_lfq_node_rcu *node;
+
+       /* We need to reallocate to protect from ABA. */
+       node = make_dummy(q, NULL);
+       _cds_lfq_enqueue_rcu(q, node);
+}
+
 /*
- * Should be called under rcu read lock critical section.
+ * Acts as a RCU reader.
  *
  * The caller must wait for a grace period to pass before freeing the returned
  * node or modifying the cds_lfq_node_rcu structure.
@@ -178,50 +194,36 @@ struct cds_lfq_node_rcu *_cds_lfq_dequeue_rcu(struct cds_lfq_queue_rcu *q)
        for (;;) {
                struct cds_lfq_node_rcu *head, *next;
 
+               rcu_read_lock();
                head = rcu_dereference(q->head);
                next = rcu_dereference(head->next);
-               if (is_dummy(q, head) && next == NULL)
+               if (head->dummy && next == NULL) {
+                       rcu_read_unlock();
                        return NULL;    /* empty */
+               }
                /*
                 * We never, ever allow dequeue to get to a state where
                 * the queue is empty (we need at least one node in the
                 * queue). This is ensured by checking if the head next
-                * is NULL and retry in that case (this means a
-                * concurrent dummy node re-enqueue is in progress).
+                * is NULL, which means we need to enqueue a dummy node
+                * before we can hope dequeuing anything.
                 */
-               if (next) {
-                       if (uatomic_cmpxchg(&q->head, head, next) == head) {
-                               if (is_dummy(q, head)) {
-                                       struct cds_lfq_node_rcu *node;
-                                       /*
-                                        * Requeue dummy. We need to
-                                        * reallocate to protect from
-                                        * ABA.
-                                        */
-                                       rcu_free_dummy(head);
-                                       node = make_dummy(q, NULL);
-                                       /*
-                                        * We are the only thread
-                                        * allowed to update dummy (we
-                                        * own the old dummy). Other
-                                        * dequeue threads read it
-                                        * concurrently with RCU
-                                        * read-lock held, which
-                                        * protects from ABA.
-                                        */
-                                       CMM_STORE_SHARED(q->dummy, node);
-                                       _cds_lfq_enqueue_rcu(q, node);
-                                       continue;       /* try again */
-                               }
-                               return head;
-                       } else {
-                               /* Concurrently pushed, retry */
-                               continue;
-                       }
-               } else {
-                       /* Dummy node re-enqueue is in progress, retry. */
-                       continue;
+               if (!next) {
+                       enqueue_dummy(q);
+                       next = rcu_dereference(head->next);
+               }
+               if (uatomic_cmpxchg(&q->head, head, next) != head) {
+                       rcu_read_unlock();
+                       continue;       /* Concurrently pushed. */
+               }
+               if (head->dummy) {
+                       /* Free dummy after grace period. */
+                       rcu_free_dummy(head);
+                       rcu_read_unlock();
+                       continue;       /* try again */
                }
+               rcu_read_unlock();
+               return head;
        }
 }