X-Git-Url: https://git.lttng.org/?p=urcu.git;a=blobdiff_plain;f=rculfhash.c;h=3ad3618aa7297ee5403d176d5c7f0e02be504def;hp=b9f795fd1349e6b28e2ac4c1e1f0de57154adad7;hb=a767fdc348289dc37026ee3ab46d1d4102ff57f7;hpb=5f177b1c042fd3f1b746dee55a90cc503c5276ee

diff --git a/rculfhash.c b/rculfhash.c
index b9f795f..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;
@@ -923,7 +931,7 @@ int _cds_lfht_replace(struct cds_lfht *ht, unsigned long size,
 	bucket = lookup_bucket(ht, size, bit_reverse_ulong(old_node->reverse_hash));
 	_cds_lfht_gc_bucket(bucket, new_node);
 
-	assert(is_removed(rcu_dereference(old_node->next)));
+	assert(is_removed(CMM_LOAD_SHARED(old_node->next)));
 	return 0;
 }
 
@@ -1061,10 +1069,15 @@ int _cds_lfht_del(struct cds_lfht *ht, unsigned long size,
 	 * logical removal flag). Return -ENOENT if the node had
 	 * previously been removed.
 	 */
-	next = rcu_dereference(node->next);
+	next = CMM_LOAD_SHARED(node->next);	/* next is not dereferenced */
 	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.
@@ -1082,7 +1095,7 @@ int _cds_lfht_del(struct cds_lfht *ht, unsigned long size,
 	bucket = lookup_bucket(ht, size, bit_reverse_ulong(node->reverse_hash));
 	_cds_lfht_gc_bucket(bucket, node);
 
-	assert(is_removed(rcu_dereference(node->next)));
+	assert(is_removed(CMM_LOAD_SHARED(node->next)));
 	/*
 	 * Last phase: atomically exchange node->next with a version
 	 * having "REMOVAL_OWNER_FLAG" set. If the returned node->next
@@ -1510,7 +1523,7 @@ void cds_lfht_lookup(struct cds_lfht *ht, unsigned long hash,
 		}
 		node = clear_flag(next);
 	}
-	assert(!node || !is_bucket(rcu_dereference(node->next)));
+	assert(!node || !is_bucket(CMM_LOAD_SHARED(node->next)));
 	iter->node = node;
 	iter->next = next;
 }
@@ -1543,7 +1556,7 @@ void cds_lfht_next_duplicate(struct cds_lfht *ht, cds_lfht_match_fct match,
 		}
 		node = clear_flag(next);
 	}
-	assert(!node || !is_bucket(rcu_dereference(node->next)));
+	assert(!node || !is_bucket(CMM_LOAD_SHARED(node->next)));
 	iter->node = node;
 	iter->next = next;
 }
@@ -1565,7 +1578,7 @@ void cds_lfht_next(struct cds_lfht *ht, struct cds_lfht_iter *iter)
 		}
 		node = clear_flag(next);
 	}
-	assert(!node || !is_bucket(rcu_dereference(node->next)));
+	assert(!node || !is_bucket(CMM_LOAD_SHARED(node->next)));
 	iter->node = node;
 	iter->next = next;
 }
@@ -1668,7 +1681,7 @@ int cds_lfht_del(struct cds_lfht *ht, struct cds_lfht_node *node)
 
 int cds_lfht_is_node_deleted(struct cds_lfht_node *node)
 {
-	return is_removed(rcu_dereference(node->next));
+	return is_removed(CMM_LOAD_SHARED(node->next));
 }
 
 static