Replace non-loop usage of atomic_compare_exchange_weak with strong variant

While testing BIND 9 on arm64 8+ core machine, it was discovered that
the weak variants in fact does spuriously fail, we haven't observed that
on other architectures.

This commit replaces all non-loop usage of atomic_compare_exchange_weak
with atomic_compare_exchange_strong.

lib/isc/app.c

@@ -228,8 +228,6 @@ isc_result_t
 isc_app_ctxrun(isc_appctx_t *ctx) {
 	isc_event_t *event, *next_event;
 	isc_task_t *task;
-	bool exp_false = false;
-	bool exp_true = true;
 
 	REQUIRE(VALID_APPCTX(ctx));
 
@@ -237,8 +235,8 @@ isc_app_ctxrun(isc_appctx_t *ctx) {
 	REQUIRE(main_thread == GetCurrentThread());
 #endif /* ifdef WIN32 */
 
-	if (atomic_compare_exchange_weak_acq_rel(&ctx->running, &exp_false,
+	if (atomic_compare_exchange_strong_acq_rel(
-						 true) == true)
+		    &ctx->running, &(bool){ false }, true) == true)
 	{
 		/*
 		 * Post any on-run events (in FIFO order).
@@ -344,9 +342,9 @@ isc_app_ctxrun(isc_appctx_t *ctx) {
 			}
 		}
 #endif /* WIN32 */
-		exp_true = true;
+		if (atomic_compare_exchange_strong_acq_rel(
-		if (atomic_compare_exchange_weak_acq_rel(&ctx->want_reload,
+			    &ctx->want_reload, &(bool){ true }, false))
-							 &exp_true, false)) {
+		{
 			return (ISC_R_RELOAD);
 		}
 
@@ -363,10 +361,9 @@ isc_app_ctxrun(isc_appctx_t *ctx) {
 isc_result_t
 isc_app_run(void) {
 	isc_result_t result;
-	bool exp_false = false;
 
-	REQUIRE(atomic_compare_exchange_weak_acq_rel(&is_running, &exp_false,
+	REQUIRE(atomic_compare_exchange_strong_acq_rel(
-						     true) == true);
+			&is_running, &(bool){ false }, true) == true);
 	result = isc_app_ctxrun(&isc_g_appctx);
 	atomic_store_release(&is_running, false);
 
@@ -380,8 +377,6 @@ isc_app_isrunning() {
 
 void
 isc_app_ctxshutdown(isc_appctx_t *ctx) {
-	bool exp_false = false;
-
 	REQUIRE(VALID_APPCTX(ctx));
 
 	REQUIRE(atomic_load_acquire(&ctx->running));
@@ -389,8 +384,8 @@ isc_app_ctxshutdown(isc_appctx_t *ctx) {
 	/* If ctx->shutdown_requested == true, we are already shutting
 	 * down and we want to just bail out.
 	 */
-	if (atomic_compare_exchange_weak_acq_rel(&ctx->shutdown_requested,
+	if (atomic_compare_exchange_strong_acq_rel(&ctx->shutdown_requested,
-						 &exp_false, true))
+						   &(bool){ false }, true))
 	{
 #ifdef WIN32
 		SetEvent(ctx->hEvents[SHUTDOWN_EVENT]);
@@ -480,10 +475,9 @@ isc_app_finish(void) {
 
 void
 isc_app_block(void) {
-	bool exp_false = false;
 	REQUIRE(atomic_load_acquire(&isc_g_appctx.running));
-	REQUIRE(atomic_compare_exchange_weak_acq_rel(&isc_g_appctx.blocked,
+	REQUIRE(atomic_compare_exchange_strong_acq_rel(&isc_g_appctx.blocked,
-						     &exp_false, true));
+						       &(bool){ false }, true));
 
 #ifdef WIN32
 	blockedthread = GetCurrentThread();
@@ -499,11 +493,9 @@ isc_app_block(void) {
 
 void
 isc_app_unblock(void) {
-	bool exp_true = true;
-
 	REQUIRE(atomic_load_acquire(&isc_g_appctx.running));
-	REQUIRE(atomic_compare_exchange_weak_acq_rel(&isc_g_appctx.blocked,
+	REQUIRE(atomic_compare_exchange_strong_acq_rel(&isc_g_appctx.blocked,
-						     &exp_true, false));
+						       &(bool){ true }, false));
 
 #ifdef WIN32
 	REQUIRE(blockedthread == GetCurrentThread());

lib/isc/rwlock.c

@@ -400,14 +400,10 @@ isc__rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 			break;
 		}
 
-		while (1) {
+		while (!atomic_compare_exchange_weak_acq_rel(
-			int_fast32_t zero = 0;
+			&rwl->cnt_and_flag, &(int_fast32_t){ 0 },
-			if (atomic_compare_exchange_weak_acq_rel(
+			WRITER_ACTIVE))
-				    &rwl->cnt_and_flag, &zero, WRITER_ACTIVE))
+		{
-			{
-				break;
-			}
-
 			/* Another active reader or writer is working. */
 			LOCK(&rwl->lock);
 			if (atomic_load_acquire(&rwl->cnt_and_flag) != 0) {
@@ -494,8 +490,8 @@ isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 	} else {
 		/* Try locking without entering the waiting queue. */
 		int_fast32_t zero = 0;
-		if (!atomic_compare_exchange_weak_acq_rel(&rwl->cnt_and_flag,
+		if (!atomic_compare_exchange_strong_acq_rel(
-							  &zero, WRITER_ACTIVE))
+			    &rwl->cnt_and_flag, &zero, WRITER_ACTIVE))
 		{
 			return (ISC_R_LOCKBUSY);
 		}
@@ -519,28 +515,26 @@ isc_result_t
 isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
 	REQUIRE(VALID_RWLOCK(rwl));
 
-	{
+	int_fast32_t reader_incr = READER_INCR;
-		int_fast32_t reader_incr = READER_INCR;
 
-		/* Try to acquire write access. */
+	/* Try to acquire write access. */
-		atomic_compare_exchange_weak_acq_rel(
+	atomic_compare_exchange_strong_acq_rel(&rwl->cnt_and_flag, &reader_incr,
-			&rwl->cnt_and_flag, &reader_incr, WRITER_ACTIVE);
+					       WRITER_ACTIVE);
+	/*
+	 * There must have been no writer, and there must have
+	 * been at least one reader.
+	 */
+	INSIST((reader_incr & WRITER_ACTIVE) == 0 &&
+	       (reader_incr & ~WRITER_ACTIVE) != 0);
+
+	if (reader_incr == READER_INCR) {
 		/*
-		 * There must have been no writer, and there must have
+		 * We are the only reader and have been upgraded.
-		 * been at least one reader.
+		 * Now jump into the head of the writer waiting queue.
 		 */
-		INSIST((reader_incr & WRITER_ACTIVE) == 0 &&
+		atomic_fetch_sub_release(&rwl->write_completions, 1);
-		       (reader_incr & ~WRITER_ACTIVE) != 0);
+	} else {
-
+		return (ISC_R_LOCKBUSY);
-		if (reader_incr == READER_INCR) {
-			/*
-			 * We are the only reader and have been upgraded.
-			 * Now jump into the head of the writer waiting queue.
-			 */
-			atomic_fetch_sub_release(&rwl->write_completions, 1);
-		} else {
-			return (ISC_R_LOCKBUSY);
-		}
 	}
 
 	return (ISC_R_SUCCESS);