X-Git-Url: https://git.lttng.org/?p=urcu.git;a=blobdiff_plain;f=rculfhash.c;h=3ad3618aa7297ee5403d176d5c7f0e02be504def;hp=b26a69085c35cbbf86d173193920c9e51f3b9e68;hb=a767fdc348289dc37026ee3ab46d1d4102ff57f7;hpb=a85eff522c253434a9c2b53d6c3a702842fb1d5d

diff --git a/rculfhash.c b/rculfhash.c
index b26a690..3ad3618 100644
--- a/rculfhash.c
+++ b/rculfhash.c
@@ -734,12 +734,6 @@ int is_removed(struct cds_lfht_node *node)
 	return ((unsigned long) node) & REMOVED_FLAG;
 }
 
-static
-struct cds_lfht_node *flag_removed(struct cds_lfht_node *node)
-{
-	return (struct cds_lfht_node *) (((unsigned long) node) | REMOVED_FLAG);
-}
-
 static
 int is_bucket(struct cds_lfht_node *node)
 {
@@ -764,6 +758,12 @@ struct cds_lfht_node *flag_removal_owner(struct cds_lfht_node *node)
 	return (struct cds_lfht_node *) (((unsigned long) node) | REMOVAL_OWNER_FLAG);
 }
 
+static
+struct cds_lfht_node *flag_removed_or_removal_owner(struct cds_lfht_node *node)
+{
+	return (struct cds_lfht_node *) (((unsigned long) node) | REMOVED_FLAG | REMOVAL_OWNER_FLAG);
+}
+
 static
 struct cds_lfht_node *get_end(void)
 {
@@ -894,6 +894,12 @@ int _cds_lfht_replace(struct cds_lfht *ht, unsigned long size,
 		}
 		assert(old_next == clear_flag(old_next));
 		assert(new_node != old_next);
+		/*
+		 * REMOVAL_OWNER flag is _NEVER_ set before the REMOVED
+		 * flag. It is either set atomically at the same time
+		 * (replace) or after (del).
+		 */
+		assert(!is_removal_owner(old_next));
 		new_node->next = old_next;
 		/*
 		 * Here is the whole trick for lock-free replace: we add
@@ -906,10 +912,12 @@ int _cds_lfht_replace(struct cds_lfht *ht, unsigned long size,
 		 * the old node, but will not see the new one.
 		 * This is a replacement of a node with another node
 		 * that has the same value: we are therefore not
-		 * removing a value from the hash table.
+		 * removing a value from the hash table. We set both the
+		 * REMOVED and REMOVAL_OWNER flags atomically so we own
+		 * the node after successful cmpxchg.
 		 */
 		ret_next = uatomic_cmpxchg(&old_node->next,
-			      old_next, flag_removed(new_node));
+			old_next, flag_removed_or_removal_owner(new_node));
 		if (ret_next == old_next)
 			break;		/* We performed the replacement. */
 		old_next = ret_next;
@@ -1065,6 +1073,11 @@ int _cds_lfht_del(struct cds_lfht *ht, unsigned long size,
 	if (caa_unlikely(is_removed(next)))
 		return -ENOENT;
 	assert(!is_bucket(next));
+	/*
+	 * The del operation semantic guarantees a full memory barrier
+	 * before the uatomic_or atomic commit of the deletion flag.
+	 */
+	cmm_smp_mb__before_uatomic_or();
 	/*
 	 * We set the REMOVED_FLAG unconditionally. Note that there may
 	 * be more than one concurrent thread setting this flag.