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 a232b6707d9804e0f5c40ca639df6e86d149989d..f184bea574ab72be6ff94eee58fbbfe1e12c83ff 100644 (file)
--- a/lib/dns/zone.c
+++ b/lib/dns/zone.c
@@ -1938,8 +1938,11 @@ 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)
@@ -1956,7 +1959,6 @@ 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);
@@ -1967,6 +1969,7 @@ 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);
 }