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 12875f90a0c84e4a34a63c3b3948dc659cf9b3a0..7de830f3a24c44949583913901540d5dfdf9bb62 100644 (file)
--- a/lib/dns/zone.c
+++ b/lib/dns/zone.c
@@ -2211,8 +2211,11 @@ 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)
@@ -2229,7 +2232,6 @@ 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);
@@ -2240,6 +2242,7 @@ 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);
 }