Use RCU for rad name

The RAD/agent domain is a functionality from RFC 9567 that provides
a suffix for reporting error messages. On every query context reset,
we need to check if a RAD is configured and, if so, copy it.

Since we allow the RAD to be changed by reconfiguring the zone,
this access is currently protected by a mutex, which causes contention.

This commit replaces the mutex with RCU to reduce contention. The
change results in a 3% performance improvement in the 1M delegation
test.

diff --git a/lib/dns/zone.c b/lib/dns/zone.c
index 7371e175262eb680009fbcc0c698760965c880a4..86eda3409f9554cd04c34c2d2a39e4bc8ef054d8 100644 (file)
--- a/lib/dns/zone.c
+++ b/lib/dns/zone.c
@@ -261,6 +261,20 @@ struct dns_keymgmt {
  */
 #define DNS_KEYMGMT_HASH_BITS 12
 
+typedef struct dns_rad {
+       isc_mem_t *mctx;
+       struct rcu_head rcu_head;
+       dns_fixedname_t fname;
+} dns_rad_t;
+
+static void
+free_rad_rcu(struct rcu_head *rcu_head) {
+       dns_rad_t *rad = caa_container_of(rcu_head, dns_rad_t, rcu_head);
+       dns_fixedname_invalidate(&rad->fname);
+
+       isc_mem_putanddetach(&rad->mctx, rad, sizeof(*rad));
+}
+
 struct dns_zone {
        /* Unlocked */
        unsigned int magic;
@@ -283,7 +297,7 @@ struct dns_zone {
        isc_timer_t *timer;
        isc_refcount_t irefs;
        dns_name_t origin;
-       dns_name_t rad;
+       dns_rad_t *rad;
        char *masterfile;
        char *initfile;
        const FILE *stream;                  /* loading from a stream? */
@@ -1173,7 +1187,6 @@ dns_zone_create(dns_zone_t **zonep, isc_mem_t *mctx, unsigned int tid) {
        isc_refcount_init(&zone->references, 1);
        isc_refcount_init(&zone->irefs, 0);
        dns_name_init(&zone->origin);
-       dns_name_init(&zone->rad);
        isc_sockaddr_any(&zone->notifysrc4);
        isc_sockaddr_any6(&zone->notifysrc6);
        isc_sockaddr_any(&zone->parentalsrc4);
@@ -1344,9 +1357,9 @@ zone_free(dns_zone_t *zone) {
        if (dns_name_dynamic(&zone->origin)) {
                dns_name_free(&zone->origin, zone->mctx);
        }
-       if (dns_name_dynamic(&zone->rad)) {
-               dns_name_free(&zone->rad, zone->mctx);
-       }
+
+       dns_zone_setrad(zone, NULL);
+
        if (zone->strnamerd != NULL) {
                isc_mem_free(zone->mctx, zone->strnamerd);
        }
@@ -24520,12 +24533,15 @@ dns_zone_getrad(dns_zone_t *zone, dns_name_t *name) {
        REQUIRE(DNS_ZONE_VALID(zone));
        REQUIRE(DNS_NAME_VALID(name));
 
-       LOCK_ZONE(zone);
-       if (dns_name_dynamic(&zone->rad)) {
-               dns_name_copy(&zone->rad, name);
+       rcu_read_lock();
+       dns_rad_t *rad = rcu_dereference(zone->rad);
+       if (rad != NULL) {
+               dns_name_t *inner = dns_fixedname_name(&rad->fname);
+               dns_name_copy(inner, name);
                result = ISC_R_SUCCESS;
        }
-       UNLOCK_ZONE(zone);
+       rcu_read_unlock();
+
        return result;
 }
 
@@ -24534,12 +24550,20 @@ dns_zone_setrad(dns_zone_t *zone, dns_name_t *name) {
        REQUIRE(DNS_ZONE_VALID(zone));
        REQUIRE(name == NULL || DNS_NAME_VALID(name));
 
-       LOCK_ZONE(zone);
-       if (dns_name_dynamic(&zone->rad)) {
-               dns_name_free(&zone->rad, zone->mctx);
-       }
+       rcu_read_lock();
+       dns_rad_t *new_rad = NULL;
        if (name != NULL) {
-               dns_name_dup(name, zone->mctx, &zone->rad);
+               new_rad = isc_mem_get(zone->mctx, sizeof(*new_rad));
+               *new_rad = (dns_rad_t){};
+               dns_fixedname_init(&new_rad->fname);
+
+               isc_mem_attach(zone->mctx, &new_rad->mctx);
+               dns_name_copy(name, dns_fixedname_name(&new_rad->fname));
        }
-       UNLOCK_ZONE(zone);
+       dns_rad_t *xchg_rad = rcu_xchg_pointer(&zone->rad, new_rad);
+
+       if (xchg_rad != NULL) {
+               call_rcu(&xchg_rad->rcu_head, free_rad_rcu);
+       }
+       rcu_read_unlock();
 }