Added some synchronization to ns and zdb modules.

The synchronization needs revision and some thorough testing!

src/server/name-server.c

@@ -5,6 +5,8 @@
 #include <stdio.h>
 #include <assert.h>
 
+#include <urcu.h>
+
 //#define NS_DEBUG
 
 /*----------------------------------------------------------------------------*/
@@ -37,15 +39,16 @@ int ns_answer_request( ns_nameserver *nameserver, const char *query_wire,
            query->questions[0].qname);
     debug_ns_hex(query->questions[0].qname, strlen(query->questions[0].qname));
 
-//    const ck_hash_table_item *item = ck_find_item(
-//            table, query->questions[0].qname,
-//            strlen(query->questions[0].qname));
+	// start of RCU read critical section (getting the node from the database)
+	rcu_read_lock();
+
     const zn_node *node =
             zdb_find_name(nameserver->zone_db, query->questions[0].qname);
 
     dnss_packet *response = dnss_create_empty_packet();
     if (response == NULL) {
         dnss_destroy_packet(&query);
+		rcu_read_unlock();
         return -1;
     }
 
@@ -54,6 +57,7 @@ int ns_answer_request( ns_nameserver *nameserver, const char *query_wire,
         if (dnss_create_response(query, NULL, 0, &response) != 0) {
             dnss_destroy_packet(&query);
             dnss_destroy_packet(&response);
+			rcu_read_unlock();
             return -1;
         }
     } else {
@@ -63,10 +67,15 @@ int ns_answer_request( ns_nameserver *nameserver, const char *query_wire,
                                  1, &response) != 0) {
             dnss_destroy_packet(&query);
             dnss_destroy_packet(&response);
+			rcu_read_unlock();
             return -1;
         }
     }
 
+	// end of RCU read critical section (all data copied)
+	node = NULL;
+	rcu_read_unlock();
+
     debug_ns("Response ID: %u\n", response->header.id);
 
     if (dnss_wire_format(response, response_wire, rsize) != 0) {

src/server/zone-database.c

@@ -4,6 +4,8 @@
 #include <stdio.h>
 #include <assert.h>
 
+#include <urcu.h>
+
 /*----------------------------------------------------------------------------*/
 
 zdb_database *zdb_create()
@@ -24,6 +26,9 @@ zdb_database *zdb_create()
 int zdb_create_zone( zdb_database *database, dnss_dname_wire zone_name,
                      uint items )
 {
+	// add some lock to avoid multiple zone creations?
+	// add some check if the zone is not already in db?
+
     zdb_zone *zone = malloc(sizeof(zdb_zone));
 
     if (zone == NULL) {
@@ -63,17 +68,37 @@ void zdb_find_zone( zdb_database *database, dnss_dname_wire zone_name,
     *zone = database->head;
     *prev = NULL;
 
+	// start of RCU reader critical section
+	rcu_read_lock();
+
     while ((*zone) != NULL
            && dnss_dname_wire_cmp((*zone)->zone_name, zone_name) != 0) {
         (*prev) = (*zone);
         (*zone) = (*zone)->next;
     }
+
+	// end of RCU reader critical section
+	rcu_read_unlock();
+}
+
+/*----------------------------------------------------------------------------*/
+
+void zdb_disconnect_zone( zdb_database *database, zdb_zone *z, zdb_zone *prev )
+{
+	// disconect the zone from the list
+	if (prev != NULL) {
+		prev->next = z->next;
+	} else {
+		database->head = z->next;
+	}
 }
 
 /*----------------------------------------------------------------------------*/
 
 int zdb_remove_zone( zdb_database *database, dnss_dname_wire zone_name )
 {
+	// add some lock to avoid multiple removals
+
     zdb_zone *z = NULL, *zp = NULL;
     zdb_find_zone(database, zone_name, &z, &zp);
 
@@ -82,18 +107,15 @@ int zdb_remove_zone( zdb_database *database, dnss_dname_wire zone_name )
         return -1;
     }
 
-    // disconect the zone from the list
-    if (zp != NULL) {
-        zp->next = z->next;
-    } else {
-        database->head = z->next;
-    }
+	zdb_disconnect_zone(database, z, zp);
+
+	// wait for all readers to finish
+	synchronize_rcu();
 
     zds_destroy(&z->zone);
     assert(z->zone == NULL);
     dnss_dname_wire_destroy(&z->zone_name);
     assert(z->zone_name == NULL);
-
     free(z);
 
     return 0;
@@ -105,6 +127,10 @@ int zdb_insert_name( zdb_database *database, dnss_dname_wire zone_name,
                      dnss_dname_wire dname, zn_node *node )
 {
     zdb_zone *z = NULL, *zp = NULL;
+
+	// start of RCU reader critical section (the zone should not be removed)
+	rcu_read_lock();
+
     zdb_find_zone(database, zone_name, &z, &zp);
 
     if (z == NULL) {
@@ -115,7 +141,11 @@ int zdb_insert_name( zdb_database *database, dnss_dname_wire zone_name,
     debug_zdb("Found zone: ");
     debug_zdb_hex(z->zone_name, strlen(z->zone_name) + 1);
 
-    return zds_insert(z->zone, dname, node);
+	int res = zds_insert(z->zone, dname, node);
+
+	// end of RCU reader critical section
+	rcu_read_unlock();
+	return res;
 }
 
 /*----------------------------------------------------------------------------*/
@@ -126,6 +156,10 @@ zdb_zone *zdb_find_zone_for_name( zdb_database *database,
     zdb_zone *z = database->head, *best = NULL;
     uint most_matched = 0;
 
+	// start of RCU reader critical section
+	// maybe not needed, called only from zdb_find_name()
+	rcu_read_lock();
+
     while (z != NULL) {
         uint matched = dnss_dname_wire_match(&dname, &z->zone_name);
         if (matched > most_matched) {
@@ -135,6 +169,9 @@ zdb_zone *zdb_find_zone_for_name( zdb_database *database,
         z = z->next;
     }
 
+	// end of RCU reader critical section
+	rcu_read_unlock();
+
     return best;
 }
 
@@ -142,6 +179,9 @@ zdb_zone *zdb_find_zone_for_name( zdb_database *database,
 
 const zn_node *zdb_find_name( zdb_database *database, dnss_dname_wire dname )
 {
+	// start of RCU reader critical section
+	rcu_read_lock();
+
     zdb_zone *z = zdb_find_zone_for_name(database, dname);
 
     if (z == NULL) {
@@ -152,21 +192,31 @@ const zn_node *zdb_find_name( zdb_database *database, dnss_dname_wire dname )
     debug_zdb("Found zone: ");
     debug_zdb_hex(z->zone_name, strlen(z->zone_name) + 1);
 
-    return zds_find(z->zone, dname);
+	const zn_node *found = zds_find(z->zone, dname);
+
+	// end of RCU reader critical section
+	rcu_read_unlock();
+
+	return found;
 }
 
 /*----------------------------------------------------------------------------*/
 
 void zdb_destroy( zdb_database **database )
 {
-    zdb_zone *z = (*database)->head;
-    zdb_zone *zp = NULL;
-
-    while (z != NULL) {
-        zp = z;
-        z = z->next;
-        zds_destroy(&zp->zone);
-        dnss_dname_wire_destroy(&zp->zone_name);
-        free(zp);
+	// add some lock to avoid multiple destroys
+
+	zdb_zone *z;
+
+	while ((*database)->head != NULL) {
+		z = (*database)->head;
+		// disconnect the first zone
+		(*database)->head = z->next;
+		// wait for all readers to finish
+		synchronize_rcu();
+		// destroy zone
+		zds_destroy(&z->zone);
+		dnss_dname_wire_destroy(&z->zone_name);
+		free(z);
     }
 }