From 4e1faa35d502cdaf9214e9f00407c9e06500d7c4 Mon Sep 17 00:00:00 2001
From: Mark Andrews <marka@isc.org>
Date: Fri, 17 Sep 2021 12:55:07 +1000
Subject: [PATCH] Pause the dbiterator before calling dns_db_find

zone.c:integrity_checks() acquires a read lock while iterating the
zone database, and calls zone_check_mx() which acquires another
read lock. If another thread tries to acquire a write lock in the
meantime, it can deadlock. Calling dns_dbiterator_pause() to release
the first read lock prevents this.
---
 lib/dns/zone.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/dns/zone.c b/lib/dns/zone.c
index 5235e1b610..7bd8c05c9b 100644
--- a/lib/dns/zone.c
+++ b/lib/dns/zone.c
@@ -3326,6 +3326,8 @@ integrity_checks(dns_zone_t *zone, dns_db_t *db) {
 			goto next;
 		}
 
+		dns_dbiterator_pause(dbiterator);
+
 		/*
 		 * Don't check the NS records at the origin.
 		 */