From: Ondřej Surý <ondrej@isc.org>
Date: Tue, 4 Feb 2025 17:02:29 +0000 (+0100)
Subject: Rely on call_rcu() to destroy the qpzone outside of locks
X-Git-Tag: v9.21.5~3^2~1
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1fa5219fdfdec78d71b9fc270f87fa068a98f2a6;p=thirdparty%2Fbind9.git

Rely on call_rcu() to destroy the qpzone outside of locks

Reduce the number of qpzone_ref() and qpzone_unref() calls in
qpzone_detachnode() by relying on the call_rcu to delay
the destruction of the lock buckets.
---

diff --git a/lib/dns/qpcache.c b/lib/dns/qpcache.c
index 74bdba0223b..c59d4e0f95c 100644
--- a/lib/dns/qpcache.c
+++ b/lib/dns/qpcache.c
@@ -28,7 +28,7 @@
 #include <isc/loop.h>
 #include <isc/mem.h>
 #include <isc/mutex.h>
-#include <isc/once.h>
+#include <isc/os.h>
 #include <isc/queue.h>
 #include <isc/random.h>
 #include <isc/refcount.h>
diff --git a/lib/dns/qpzone.c b/lib/dns/qpzone.c
index 97071b6019c..a1b7b97a207 100644
--- a/lib/dns/qpzone.c
+++ b/lib/dns/qpzone.c
@@ -28,7 +28,7 @@
 #include <isc/loop.h>
 #include <isc/mem.h>
 #include <isc/mutex.h>
-#include <isc/once.h>
+#include <isc/os.h>
 #include <isc/random.h>
 #include <isc/refcount.h>
 #include <isc/result.h>
@@ -3939,17 +3939,15 @@ detachnode(dns_db_t *db, dns_dbnode_t **nodep DNS__DB_FLARG) {
 	nlock = &qpdb->buckets[node->locknum].lock;
 
 	/*
-	 * We can't destroy qpzonedb while holding a nodelock, so
-	 * we need to reference it before acquiring the lock
-	 * and release it afterward.
+	 * qpzone_destroy() uses call_rcu() API to destroy the node locks,
+	 * so it is safe to call it in the middle of NODE_LOCK.
 	 */
-	qpzonedb_ref(qpdb);
 
+	rcu_read_lock();
 	NODE_RDLOCK(nlock, &nlocktype);
 	qpznode_release(qpdb, node, 0, &nlocktype DNS__DB_FLARG_PASS);
 	NODE_UNLOCK(nlock, &nlocktype);
-
-	qpzonedb_detach(&qpdb);
+	rcu_read_unlock();
 }
 
 static unsigned int