Use LDAP_OPT_KEEPCONN to prevent the target connection from being freed

On error, the ldap connection was freed and under some circumstances the fd was being reused,
which caused an assertion error in connection_init.

servers/slapd/back-asyncmeta/conn.c

@@ -182,6 +182,9 @@ asyncmeta_init_one_conn(
 		       op->o_log_prefix, rs->sr_err );
 		goto error_return;
 	}
+
+	ldap_set_option( msc->msc_ld, LDAP_OPT_KEEPCONN, LDAP_OPT_ON);
+
 	msc->msc_ldr = ldap_dup(msc->msc_ld);
 	if (!msc->msc_ldr) {
 		ldap_ld_free(msc->msc_ld, 0, NULL, NULL);
@@ -1037,7 +1040,7 @@ int asyncmeta_start_one_listener(a_metaconn_t *mc,
 
 	msc = &mc->mc_conns[candidate];
 	if ( slapd_shutdown || !META_BACK_CONN_INITED( msc ) || msc->msc_ld == NULL
-	    || !META_IS_CANDIDATE( &candidates[ candidate ] )) {
+	    || META_BACK_CONN_INVALID(msc) || !META_IS_CANDIDATE( &candidates[ candidate ] )) {
 		return LDAP_SUCCESS;
 	}
 	bc->msgids[candidate] = candidates[candidate].sr_msgid;

servers/slapd/back-asyncmeta/meta_result.c

@@ -1510,6 +1510,7 @@ again:
 		if (rc < 1) {
 			if (rc < 0) {
 				ldap_get_option( mc->mc_conns[i].msc_ldr, LDAP_OPT_ERROR_NUMBER, &rc);
+				META_BACK_CONN_INVALID_SET(&mc->mc_conns[i]);
 				asyncmeta_op_read_error(mc, i, rc, ctx);
 			}
 			ldap_pvt_thread_mutex_lock( &mc->mc_om_mutex );
@@ -1626,9 +1627,12 @@ retry_bc:
 	slap_sl_mem_setctx(ctx, oldctx);
 	if (mc->mc_conns) {
 		ldap_pvt_thread_mutex_lock( &mc->mc_om_mutex );
-		for (i=0; i<ntargets; i++)
-			if (mc->mc_conns[i].msc_ldr && mc->mc_conns[i].conn)
+		for (i=0; i<ntargets; i++) {
+			if (!slapd_shutdown && !META_BACK_CONN_INVALID(msc)
+			    && mc->mc_conns[i].msc_ldr && mc->mc_conns[i].conn) {
 				connection_client_enable(mc->mc_conns[i].conn);
+			}
+		}
 		ldap_pvt_thread_mutex_unlock( &mc->mc_om_mutex );
 	}
 	return NULL;