From: Your Name <alessio@isc.org>
Date: Fri, 25 Apr 2025 08:41:29 +0000 (+0200)
Subject: Call rcu_barrier earlier in the destructor
X-Git-Tag: v9.21.8~10^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=59086c33e2edb9ebc4f5b5bc6cde35f851a6f45b;p=thirdparty%2Fbind9.git

Call rcu_barrier earlier in the destructor

If a call_rcu thread is running, there is a possible race condition
where the destructors run before all call_rcu callbacks have finished
running. This can happen, for example, if the call_rcu callback tries to
log something after the logging context has been torn down.

In !10394, we tried to counter this by explicitely creating a call_rcu
thread an shutting it down before running the destructors, but it is
possible for things to "slip" and end up on the default call_rcu thread.

As a quickfix, this commit moves an rcu_barrier() that was in the mem
context destructor earlier, so that it "protects" all libisc
destructors.
---

diff --git a/lib/isc/lib.c b/lib/isc/lib.c
index bdff8efd358..c0f9d30dba4 100644
--- a/lib/isc/lib.c
+++ b/lib/isc/lib.c
@@ -67,6 +67,9 @@ isc__lib_shutdown(void) {
 		return;
 	}
 
+	rcu_barrier();
+	rcu_unregister_thread();
+
 	isc__iterated_hash_shutdown();
 	isc__xml_shutdown();
 	isc__uv_shutdown();
@@ -75,6 +78,4 @@ isc__lib_shutdown(void) {
 	isc__mem_shutdown();
 	isc__mutex_shutdown();
 	isc__os_shutdown();
-	/* should be after isc__mem_shutdown() which calls rcu_barrier() */
-	rcu_unregister_thread();
 }
diff --git a/lib/isc/mem.c b/lib/isc/mem.c
index c1b0ab7331c..ff34485ae0e 100644
--- a/lib/isc/mem.c
+++ b/lib/isc/mem.c
@@ -434,10 +434,9 @@ isc__mem_initialize(void) {
 
 void
 isc__mem_shutdown(void) {
+	/* should be called after an rcu_barrier() */
 	bool empty;
 
-	rcu_barrier();
-
 	isc__mem_checkdestroyed();
 
 	LOCK(&contextslock);