Convert slabtop to use the cds_list

This is the first commit in series that aims to reduce the node locking
by replacing the single-linked list of slabtop(s) with CDS linked list.
This commit doesn't do anything else beyond replacing .next link with
the cds_list_head.  RCU semantics is going to be added in the subsequent
commits.

lib/dns/include/dns/rdataslab.h

@@ -64,15 +64,18 @@ struct dns_slabheader_proof {
 	dns_rdatatype_t type;
 };
 
-#define DNS_SLABTOP_FOREACH(elt, first)                                    \
-	for (dns_slabtop_t *elt = first,                                   \
-			   *elt##_next = (elt != NULL) ? elt->next : NULL; \
-	     elt != NULL;                                                  \
-	     elt = elt##_next, elt##_next = (elt != NULL) ? elt->next : NULL)
+#define DNS_SLABTOP_FOREACH(pos, head)                 \
+	dns_slabtop_t *pos = NULL, *pos##_next = NULL; \
+	cds_list_for_each_entry_safe(pos, pos##_next, head, types_link)
+
+#define DNS_SLABTOP_FOREACH_FROM(pos, head, first)      \
+	dns_slabtop_t *pos = first, *pos##_next = NULL; \
+	cds_list_for_each_entry_safe_from(pos, pos##_next, head, types_link)
 
 typedef struct dns_slabtop dns_slabtop_t;
 struct dns_slabtop {
-	dns_slabtop_t	 *next;
+	struct cds_list_head types_link;
+
 	dns_slabheader_t *header;
 	dns_typepair_t	  typepair;
 

lib/dns/qpcache.c

@@ -157,7 +157,8 @@ struct qpcnode {
 	isc_refcount_t references;
 	isc_refcount_t erefs;
 
-	dns_slabtop_t *data;
+	struct cds_list_head types_list;
+	struct cds_list_head *data;
 
 	/*%
 	 * NOTE: The 'dirty' flag is protected by the node lock, so
@@ -561,8 +562,6 @@ clean_cache_headers(dns_slabtop_t *top) {
 
 static void
 clean_cache_node(qpcache_t *qpdb, qpcnode_t *node) {
-	dns_slabtop_t *top_prev = NULL;
-
 	/*
 	 * Caller must be holding the node lock.
 	 */
@@ -584,11 +583,7 @@ clean_cache_node(qpcache_t *qpdb, qpcnode_t *node) {
 		 * If current slabtop is empty, we can clean it up.
 		 */
 		if (top->header == NULL) {
-			if (top_prev != NULL) {
-				top_prev->next = top->next;
-			} else {
-				node->data = top->next;
-			}
+			cds_list_del(&top->types_link);
 
 			if (ISC_LINK_LINKED(top, link)) {
 				ISC_SIEVE_UNLINK(
@@ -596,8 +591,6 @@ clean_cache_node(qpcache_t *qpdb, qpcnode_t *node) {
 					link);
 			}
 			dns_slabtop_destroy(((dns_db_t *)qpdb)->mctx, &top);
-		} else {
-			top_prev = top;
 		}
 	}
 
@@ -750,7 +743,7 @@ qpcnode_release(qpcache_t *qpdb, qpcnode_t *node, isc_rwlocktype_t *nlocktypep,
 	}
 
 	/* Handle easy and typical case first. */
-	if (!node->dirty && node->data != NULL) {
+	if (!node->dirty && !cds_list_empty(node->data)) {
 		goto unref;
 	}
 
@@ -781,7 +774,7 @@ qpcnode_release(qpcache_t *qpdb, qpcnode_t *node, isc_rwlocktype_t *nlocktypep,
 		clean_cache_node(qpdb, node);
 	}
 
-	if (node->data != NULL) {
+	if (!cds_list_empty(node->data)) {
 		goto unref;
 	}
 
@@ -2383,6 +2376,8 @@ static qpcnode_t *
 new_qpcnode(qpcache_t *qpdb, const dns_name_t *name, dns_namespace_t nspace) {
 	qpcnode_t *newdata = isc_mem_get(qpdb->common.mctx, sizeof(*newdata));
 	*newdata = (qpcnode_t){
+		.types_list = CDS_LIST_HEAD_INIT(newdata->types_list),
+		.data = &newdata->types_list,
 		.methods = &qpcnode_methods,
 		.qpdb = qpdb,
 		.name = DNS_NAME_INITEMPTY,
@@ -2888,16 +2883,13 @@ add(qpcache_t *qpdb, qpcnode_t *qpnode, dns_slabheader_t *newheader,
 
 		if (prio_header(newtop)) {
 			/* This is a priority type, prepend it */
-			newtop->next = qpnode->data;
-			qpnode->data = newtop;
+			cds_list_add(&newtop->types_link, qpnode->data);
 		} else if (priotop != NULL) {
 			/* Append after the priority headers */
-			newtop->next = priotop->next;
-			priotop->next = newtop;
+			cds_list_add(&newtop->types_link, &priotop->types_link);
 		} else {
 			/* There were no priority headers */
-			newtop->next = qpnode->data;
-			qpnode->data = newtop;
+			cds_list_add(&newtop->types_link, qpnode->data);
 		}
 
 		if (overmaxtype(qpdb, ntypes)) {
@@ -3387,24 +3379,29 @@ rdatasetiter_next(dns_rdatasetiter_t *it DNS__DB_FLARG) {
 	qpcnode_t *qpnode = (qpcnode_t *)iterator->common.node;
 	isc_rwlocktype_t nlocktype = isc_rwlocktype_none;
 	isc_rwlock_t *nlock = &qpdb->buckets[qpnode->locknum].lock;
-	dns_slabtop_t *next = NULL;
+	dns_slabtop_t *from = NULL;
 
 	if (iterator->current == NULL) {
 		return ISC_R_NOMORE;
 	}
-	next = iterator->current->next;
-	iterator->current = NULL;
 
 	NODE_RDLOCK(nlock, &nlocktype);
 
-	DNS_SLABTOP_FOREACH(top, next) {
-		dns_slabheader_t *header = first_existing_header(top);
+	from = cds_list_entry(iterator->current->types_link.next, dns_slabtop_t,
+			      types_link);
+	iterator->current = NULL;
 
-		if (EXPIREDOK(iterator) ||
-		    (header != NULL && iterator_active(qpdb, iterator, header)))
-		{
-			iterator->current = top;
-			break;
+	if (from != NULL) {
+		DNS_SLABTOP_FOREACH_FROM(top, qpnode->data, from) {
+			dns_slabheader_t *header = first_existing_header(top);
+
+			if (EXPIREDOK(iterator) ||
+			    (header != NULL &&
+			     iterator_active(qpdb, iterator, header)))
+			{
+				iterator->current = top;
+				break;
+			}
 		}
 	}
 

lib/dns/qpzone.c

@@ -198,7 +198,9 @@ struct qpznode {
 	atomic_bool wild;
 	atomic_bool delegating;
 	atomic_bool dirty;
-	dns_slabtop_t *data;
+
+	struct cds_list_head types_list;
+	struct cds_list_head *data;
 };
 
 struct qpzonedb {
@@ -631,6 +633,8 @@ static qpznode_t *
 new_qpznode(qpzonedb_t *qpdb, const dns_name_t *name, dns_namespace_t nspace) {
 	qpznode_t *newdata = isc_mem_get(qpdb->common.mctx, sizeof(*newdata));
 	*newdata = (qpznode_t){
+		.types_list = CDS_LIST_HEAD_INIT(newdata->types_list),
+		.data = &newdata->types_list,
 		.methods = &qpznode_methods,
 		.name = DNS_NAME_INITEMPTY,
 		.nspace = nspace,
@@ -848,7 +852,6 @@ clean_multiple_versions(dns_slabtop_t *top, uint32_t least_serial) {
 
 static void
 clean_zone_node(qpznode_t *node, uint32_t least_serial) {
-	dns_slabtop_t *top_prev = NULL;
 	bool still_dirty = false;
 
 	/*
@@ -873,11 +876,7 @@ clean_zone_node(qpznode_t *node, uint32_t least_serial) {
 		check_top_header(top);
 
 		if (top->header == NULL) {
-			if (top_prev != NULL) {
-				top_prev->next = top->next;
-			} else {
-				node->data = top->next;
-			}
+			cds_list_del(&top->types_link);
 			dns_slabtop_destroy(node->mctx, &top);
 		} else {
 			/*
@@ -891,8 +890,6 @@ clean_zone_node(qpznode_t *node, uint32_t least_serial) {
 			 */
 			still_dirty = clean_multiple_versions(top,
 							      least_serial);
-
-			top_prev = top;
 		}
 	}
 	if (!still_dirty) {
@@ -942,7 +939,7 @@ qpznode_release(qpznode_t *node, uint32_t least_serial,
 	}
 
 	/* Handle easy and typical case first. */
-	if (!node->dirty && node->data != NULL) {
+	if (!node->dirty && !cds_list_empty(node->data)) {
 		goto unref;
 	}
 
@@ -1998,16 +1995,14 @@ add(qpzonedb_t *qpdb, qpznode_t *node, const dns_name_t *nodename,
 
 			if (prio_type(newheader->typepair)) {
 				/* This is a priority type, prepend it */
-				newtop->next = node->data;
-				node->data = newtop;
+				cds_list_add(&newtop->types_link, node->data);
 			} else if (priotop != NULL) {
 				/* Append after the priority headers */
-				newtop->next = priotop->next;
-				priotop->next = newtop;
+				cds_list_add(&newtop->types_link,
+					     &priotop->types_link);
 			} else {
 				/* There were no priority headers */
-				newtop->next = node->data;
-				node->data = newtop;
+				cds_list_add(&newtop->types_link, node->data);
 			}
 		}
 	}
@@ -3964,25 +3959,30 @@ rdatasetiter_next(dns_rdatasetiter_t *iterator DNS__DB_FLARG) {
 	qpz_version_t *version = (qpz_version_t *)qrditer->common.version;
 	isc_rwlocktype_t nlocktype = isc_rwlocktype_none;
 	isc_rwlock_t *nlock = qpzone_get_lock(node);
-	dns_slabtop_t *next = NULL;
+	dns_slabtop_t *from = NULL;
 
 	if (qrditer->currenttop == NULL) {
 		return ISC_R_NOMORE;
 	}
-	next = qrditer->currenttop->next;
-	qrditer->currenttop = NULL;
-	qrditer->current = NULL;
 
 	NODE_RDLOCK(nlock, &nlocktype);
 
+	from = cds_list_entry(qrditer->currenttop->types_link.next,
+			      dns_slabtop_t, types_link);
+	qrditer->currenttop = NULL;
+	qrditer->current = NULL;
+
 	/*
 	 * Find the start of the header chain for the next type.
 	 */
-	DNS_SLABTOP_FOREACH(top, next) {
-		qrditer->current = first_existing_header(top, version->serial);
-		if (qrditer->current != NULL) {
-			qrditer->currenttop = top;
-			break;
+	if (from != NULL) {
+		DNS_SLABTOP_FOREACH_FROM(top, node->data, from) {
+			qrditer->current =
+				first_existing_header(top, version->serial);
+			if (qrditer->current != NULL) {
+				qrditer->currenttop = top;
+				break;
+			}
 		}
 	}
 

lib/dns/rdataslab.c

@@ -1179,6 +1179,7 @@ dns_slabtop_t *
 dns_slabtop_new(isc_mem_t *mctx, dns_typepair_t typepair) {
 	dns_slabtop_t *top = isc_mem_get(mctx, sizeof(*top));
 	*top = (dns_slabtop_t){
+		.types_link = CDS_LIST_HEAD_INIT(top->types_link),
 		.typepair = typepair,
 		.link = ISC_LINK_INITIALIZER,
 	};

lib/isc/include/isc/urcu.h

@@ -30,6 +30,7 @@
 #include <urcu-pointer.h>
 
 #include <urcu/compiler.h>
+#include <urcu/list.h>
 #include <urcu/rculfhash.h>
 #include <urcu/rculist.h>
 #include <urcu/wfstack.h>