4228. [bug] Address race condition in dns_client_destroyrestrans.

[RT #40605]

CHANGES

@@ -1,3 +1,6 @@
+4228.	[bug]		Address race condition in dns_client_destroyrestrans.
+			[RT #40605]
+
 4227.	[bug]		Silence static analysis warnings. [RT #40828]
 
 4226.	[bug]		Address a theoretical shutdown race in

lib/dns/client.c

@@ -1178,7 +1178,6 @@ client_resfind(resctx_t *rctx, dns_fetchevent_t *event) {
 	UNLOCK(&rctx->lock);
 }
 
-
 static void
 suspend(isc_task_t *task, isc_event_t *event) {
 	isc_appctx_t *actx = event->ev_arg;
@@ -1498,6 +1497,13 @@ dns_client_destroyrestrans(dns_clientrestrans_t **transp) {
 	mctx = client->mctx;
 	dns_view_detach(&rctx->view);
 
+	/*
+	 * Wait for the lock in client_resfind to be released before
+	 * destroying the lock.
+	 */
+	LOCK(&rctx->lock);
+	UNLOCK(&rctx->lock);
+
 	LOCK(&client->lock);
 
 	INSIST(ISC_LINK_LINKED(rctx, link));