When we become primary, we connect to the remote and expect it to be in

secondary role. It is possible that the remote node is primary, but only
because there was a role change and it didn't finish cleaning up (unmounting
file systems, etc.). If we detect such situation, wait for the remote node
to switch the role to secondary before accepting I/Os. If we don't wait for
it in that case, we will most likely cause split-brain.

MFC after:	1 week

sbin/hastd/hastd.c

@@ -736,6 +736,13 @@ listen_accept(void)
 		nv_add_stringf(nverr, "errmsg",
 		    "Remote node acts as %s for the resource and not as %s.",
 		    role2str(res->hr_role), role2str(HAST_ROLE_SECONDARY));
+		if (res->hr_role == HAST_ROLE_PRIMARY) {
+			/*
+			 * If we act as primary request the other side to wait
+			 * for us for a bit, as may might be finishing cleanups.
+			 */
+			nv_add_uint8(nverr, 1, "wait");
+		}
 		goto fail;
 	}
 	/* Does token (if exists) match? */

sbin/hastd/primary.c

@@ -219,6 +219,7 @@ static pthread_cond_t range_regular_cond;
 static struct rangelocks *range_sync;
 static bool range_sync_wait;
 static pthread_cond_t range_sync_cond;
+static bool fullystarted;
 
 static void *ggate_recv_thread(void *arg);
 static void *local_send_thread(void *arg);
@@ -524,7 +525,7 @@ primary_connect(struct hast_resource *res, struct proto_conn **connp)
 	return (0);
 }
 
-static bool
+static int
 init_remote(struct hast_resource *res, struct proto_conn **inp,
     struct proto_conn **outp)
 {
@@ -537,6 +538,7 @@ init_remote(struct hast_resource *res, struct proto_conn **inp,
 	int64_t datasize;
 	uint32_t mapsize;
 	size_t size;
+	int error;
 
 	PJDLOG_ASSERT((inp == NULL && outp == NULL) || (inp != NULL && outp != NULL));
 	PJDLOG_ASSERT(real_remote(res));
@@ -545,7 +547,9 @@ init_remote(struct hast_resource *res, struct proto_conn **inp,
 	errmsg = NULL;
 
 	if (primary_connect(res, &out) == -1)
-		return (false);
+		return (ECONNREFUSED);
+
+	error = ECONNABORTED;
 
 	/*
 	 * First handshake step.
@@ -577,6 +581,8 @@ init_remote(struct hast_resource *res, struct proto_conn **inp,
 	errmsg = nv_get_string(nvin, "errmsg");
 	if (errmsg != NULL) {
 		pjdlog_warning("%s", errmsg);
+		if (nv_exists(nvin, "wait"))
+			error = EBUSY;
 		nv_free(nvin);
 		goto close;
 	}
@@ -734,14 +740,14 @@ init_remote(struct hast_resource *res, struct proto_conn **inp,
 		res->hr_remoteout = out;
 	}
 	event_send(res, EVENT_CONNECT);
-	return (true);
+	return (0);
 close:
 	if (errmsg != NULL && strcmp(errmsg, "Split-brain condition!") == 0)
 		event_send(res, EVENT_SPLITBRAIN);
 	proto_close(out);
 	if (in != NULL)
 		proto_close(in);
-	return (false);
+	return (error);
 }
 
 static void
@@ -920,8 +926,30 @@ hastd_primary(struct hast_resource *res)
 	 */
 	error = pthread_create(&td, NULL, ctrl_thread, res);
 	PJDLOG_ASSERT(error == 0);
-	if (real_remote(res) && init_remote(res, NULL, NULL))
+	if (real_remote(res)) {
-		sync_start();
+		error = init_remote(res, NULL, NULL);
+		if (error == 0) {
+			sync_start();
+		} else if (error == EBUSY) {
+			time_t start = time(NULL);
+
+			pjdlog_warning("Waiting for remote node to become %s for %ds.",
+			    role2str(HAST_ROLE_SECONDARY),
+			    res->hr_timeout);
+			for (;;) {
+				sleep(1);
+				error = init_remote(res, NULL, NULL);
+				if (error != EBUSY)
+					break;
+				if (time(NULL) > start + res->hr_timeout)
+					break;
+			}
+			if (error == EBUSY) {
+				pjdlog_warning("Remote node is still %s, starting anyway.",
+				    role2str(HAST_ROLE_PRIMARY));
+			}
+		}
+	}
 	error = pthread_create(&td, NULL, ggate_recv_thread, res);
 	PJDLOG_ASSERT(error == 0);
 	error = pthread_create(&td, NULL, local_send_thread, res);
@@ -932,6 +960,7 @@ hastd_primary(struct hast_resource *res)
 	PJDLOG_ASSERT(error == 0);
 	error = pthread_create(&td, NULL, ggate_send_thread, res);
 	PJDLOG_ASSERT(error == 0);
+	fullystarted = true;
 	(void)sync_thread(res);
 }
 
@@ -2095,7 +2124,7 @@ guard_one(struct hast_resource *res, unsigned int ncomp)
 	pjdlog_debug(2, "remote_guard: Reconnecting to %s.",
 	    res->hr_remoteaddr);
 	in = out = NULL;
-	if (init_remote(res, &in, &out)) {
+	if (init_remote(res, &in, &out) == 0) {
 		rw_wlock(&hio_remote_lock[ncomp]);
 		PJDLOG_ASSERT(res->hr_remotein == NULL);
 		PJDLOG_ASSERT(res->hr_remoteout == NULL);
@@ -2153,12 +2182,19 @@ guard_thread(void *arg)
 			break;
 		}
 
-		pjdlog_debug(2, "remote_guard: Checking connections.");
+		/*
-		now = time(NULL);
+		 * Don't check connections until we fully started,
-		if (lastcheck + HAST_KEEPALIVE <= now) {
+		 * as we may still be looping, waiting for remote node
-			for (ii = 0; ii < ncomps; ii++)
+		 * to switch from primary to secondary.
-				guard_one(res, ii);
+		 */
-			lastcheck = now;
+		if (fullystarted) {
+			pjdlog_debug(2, "remote_guard: Checking connections.");
+			now = time(NULL);
+			if (lastcheck + HAST_KEEPALIVE <= now) {
+				for (ii = 0; ii < ncomps; ii++)
+					guard_one(res, ii);
+				lastcheck = now;
+			}
 		}
 		signo = sigtimedwait(&mask, NULL, &timeout);
 	}