Fixes for liburcu-qsbr

Move registration and deregistration of the main thread from
`isc_loopmgr_run()` into `isc__initialize()` / `isc__shutdown()`:
liburcu-qsbr fails an assertion if we try to use it from an
unregistered thread, and we need to be able to use it when the
event loops are not running.

Use `rcu_assign_pointer()` and `rcu_dereference()` in qp-trie
transactions so that they properly mark threads as online. The
RCU-protected pointer is no longer declared atomic because
liburcu does not (yet) use standard C atomics.

Fix the definition of `isc_qsbr_rcu_dereference()` to return
the referenced value, and to call the right function inside
liburcu.

Change the thread sanitizer suppressions to match any variant of
`rcu_*_barrier()`

.tsan-suppress

@@ -1,4 +1,4 @@
 # be more selective with liburcu
 race:rcu_barrier
-race:rcu_memb_barrier
+race:rcu_*_barrier
 thread:*

lib/dns/qp.c

@@ -1169,8 +1169,7 @@ dns_qpmulti_commit(dns_qpmulti_t *multi, dns_qp_t **qptp) {
 	/* paired with chunk_free() */
 	isc_refcount_increment(&qp->base->refcount);
 
-	/* reader_open() below has the matching atomic_load_acquire() */
-	atomic_store_release(&multi->reader, reader); /* COMMIT */
+	rcu_assign_pointer(multi->reader, reader); /* COMMIT */
 
 	/* clean up what we can right now */
 	if (qp->transaction_mode == QP_UPDATE || QP_NEEDGC(qp)) {
@@ -1249,8 +1248,7 @@ dns_qpmulti_rollback(dns_qpmulti_t *multi, dns_qp_t **qptp) {
 static dns_qpmulti_t *
 reader_open(dns_qpmulti_t *multi, dns_qpreadable_t qpr) {
 	dns_qpreader_t *qp = dns_qpreader(qpr);
-	/* dns_qpmulti_commit() has the matching atomic_store_release() */
-	qp_node_t *reader = atomic_load_acquire(&multi->reader);
+	qp_node_t *reader = rcu_dereference(multi->reader);
 	if (reader == NULL) {
 		QP_INIT(qp, multi->writer.methods, multi->writer.uctx);
 	} else {

lib/dns/qp_p.h

@@ -549,8 +549,8 @@ struct dns_qp {
  */
 struct dns_qpmulti {
 	uint32_t magic;
-	/*% pointer to current packed reader */
-	atomic_ptr(qp_node_t) reader;
+	/*% RCU-protected pointer to current packed reader */
+	qp_node_t *reader;
 	/*% the mutex protects the rest of this structure */
 	isc_mutex_t mutex;
 	/*% ref_ptr(writer, reader_ref) == reader */

lib/isc/include/isc/urcu.h

@@ -109,12 +109,12 @@
 #define synchronize_rcu() isc_qsbr_syncronize_rcu()
 
 #define isc_qsbr_rcu_dereference(ptr)              \
-	{                                          \
+	({                                         \
 		if (!urcu_qsbr_read_ongoing()) {   \
 			urcu_qsbr_thread_online(); \
 		}                                  \
-		urcu_qsbr_dereference(ptr);        \
-	}
+		_rcu_dereference(ptr);             \
+	})
 
 #undef rcu_dereference
 #define rcu_dereference(ptr) isc_qsbr_rcu_dereference(ptr)

lib/isc/lib.c

@@ -18,6 +18,7 @@
 #include <isc/mem.h>
 #include <isc/os.h>
 #include <isc/tls.h>
+#include <isc/urcu.h>
 #include <isc/util.h>
 #include <isc/uv.h>
 #include <isc/xml.h>
@@ -51,6 +52,7 @@ isc__initialize(void) {
 	isc__md_initialize();
 	isc__iterated_hash_initialize();
 	(void)isc_os_ncpus();
+	rcu_register_thread();
 }
 
 void
@@ -63,4 +65,6 @@ isc__shutdown(void) {
 	isc__mem_shutdown();
 	isc__mutex_shutdown();
 	isc__os_shutdown();
+	/* should be after isc__mem_shutdown() which calls rcu_barrier() */
+	rcu_unregister_thread();
 }

lib/isc/loop.c

@@ -436,8 +436,6 @@ isc_loopmgr_run(isc_loopmgr_t *loopmgr) {
 
 	bool free_call_rcu_data = !create_all_cpu_call_rcu_data(0);
 
-	rcu_register_thread();
-
 	/*
 	 * The thread 0 is this one.
 	 */
@@ -453,8 +451,6 @@ isc_loopmgr_run(isc_loopmgr_t *loopmgr) {
 
 	isc_thread_main(loop_thread, &loopmgr->loops[0]);
 
-	rcu_unregister_thread();
-
 	rcu_barrier();
 
 	if (free_call_rcu_data) {

tests/libtest/qp.c

@@ -232,7 +232,7 @@ qp_test_dumpqp(dns_qp_t *qp) {
 void
 qp_test_dumpmulti(dns_qpmulti_t *multi) {
 	dns_qpreader_t qpr;
-	qp_node_t *reader = atomic_load(&multi->reader);
+	qp_node_t *reader = rcu_dereference(multi->reader);
 	dns_qpmulti_t *whence = unpack_reader(&qpr, reader);
 	dumpqp(&multi->writer, "qpmulti->writer");
 	printf("qpmulti->reader %p root_ref %u %u:%u base %p\n", reader,