Lock zone before checking whether its asynchronous load is already pending

While this is not an issue in named, which only calls
dns_zone_asyncload() from task-exclusive mode, this function is exported
by libdns and thus may in theory be concurrently called for the same
zone by multiple threads.  It also does not hurt to be consistent
locking-wise with other DNS_ZONEFLG_LOADPENDING accesses.

diff --git a/lib/dns/zone.c b/lib/dns/zone.c
index ed9ae40c7c17c74c0329973f7803d586c3423249..99a03afd0488c056bf508093092d9e98f159aac4 100644 (file)
--- a/lib/dns/zone.c
+++ b/lib/dns/zone.c
@@ -2217,8 +2217,11 @@ dns_zone_asyncload(dns_zone_t *zone, dns_zt_zoneloaded_t done, void *arg) {
                return (ISC_R_FAILURE);
 
        /* If we already have a load pending, stop now */
-       if (DNS_ZONE_FLAG(zone, DNS_ZONEFLG_LOADPENDING))
+       LOCK_ZONE(zone);
+       if (DNS_ZONE_FLAG(zone, DNS_ZONEFLG_LOADPENDING)) {
+               UNLOCK_ZONE(zone);
                return (ISC_R_ALREADYRUNNING);
+       }
 
        asl = isc_mem_get(zone->mctx, sizeof (*asl));
        if (asl == NULL)
@@ -2235,7 +2238,6 @@ dns_zone_asyncload(dns_zone_t *zone, dns_zt_zoneloaded_t done, void *arg) {
        if (e == NULL)
                CHECK(ISC_R_NOMEMORY);
 
-       LOCK_ZONE(zone);
        zone_iattach(zone, &asl->zone);
        DNS_ZONE_SETFLAG(zone, DNS_ZONEFLG_LOADPENDING);
        isc_task_send(zone->loadtask, &e);
@@ -2246,6 +2248,7 @@ dns_zone_asyncload(dns_zone_t *zone, dns_zt_zoneloaded_t done, void *arg) {
   failure:
        if (asl != NULL)
                isc_mem_put(zone->mctx, asl, sizeof (*asl));
+       UNLOCK_ZONE(zone);
        return (result);
 }