Merge branch 'ondrej-netmgr-simplify-uv_close' into 'main'

Reorder the uv_close() calls to close the socket immediately

See merge request isc-projects/bind9!6704

doc/dev/libuv.md

@@ -0,0 +1,46 @@
+<!--
+Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+
+SPDX-License-Identifier: MPL-2.0
+
+This Source Code Form is subject to the terms of the Mozilla Public
+License, v. 2.0.  If a copy of the MPL was not distributed with this
+file, you can obtain one at https://mozilla.org/MPL/2.0/.
+
+See the COPYRIGHT file distributed with this work for additional
+information regarding copyright ownership.
+-->
+
+## Libuv Notes
+
+This document describes various notes related to the using of the libuv library.
+
+### Queueing Events onto the ``uv_loop_t``
+
+The upstream documentation on [the I/O
+loop](http://docs.libuv.org/en/v1.x/design.html#the-i-o-loop) describes the
+order in which are the various handles processed.  However, it does not describe
+the order in which the loop processes the events in the same buckets, and
+because it is counterintuitive, it is described here.
+
+When scheduling the events of the same class (f.e. ``uv_*_start()`` or
+``uv_close()``), the events are executed in the LIFO order (e.g. it's a stack,
+not a queue).  The reasoning for the upstream design choice is described in [the
+upstream issue](https://github.com/libuv/libuv/issues/3582).
+
+What does this means in practice?  F.e. when closing the handles:
+
+    uv_close(&handle1, callback1);
+	uv_close(&handle2, callback2);
+
+The ``callback2()`` will be called before the ``callback1()``, so if they are
+using the same resource, the resource can be freed in the ``callback1()`` and
+not in the ``callback2()``.
+
+Same applies f.e. to the ``uv_idle_t``, if you want the ``action1()`` to execute
+before ``action2()``, the valid code would be:
+
+    uv_idle_start(&idle2, action2);
+    uv_idle_start(&idle1, action1);
+
+which is really counterintuitive.

lib/isc/netmgr/netmgr.c

@@ -665,6 +665,8 @@ nmsocket_cleanup(isc_nmsocket_t *sock, bool dofree FLARG) {
 			 "\n",
 			 sock, isc_refcount_current(&sock->references));
 
+	isc_refcount_destroy(&sock->references);
+
 	isc__nm_decstats(sock, STATID_ACTIVE);
 
 	atomic_store(&sock->destroying, true);
@@ -675,7 +677,9 @@ nmsocket_cleanup(isc_nmsocket_t *sock, bool dofree FLARG) {
 		 * so we can clean up and free the children.
 		 */
 		for (size_t i = 0; i < sock->nchildren; i++) {
-			if (!atomic_load(&sock->children[i].destroying)) {
+			REQUIRE(!atomic_load(&sock->children[i].destroying));
+			if (isc_refcount_decrement(
+				    &sock->children[i].references)) {
 				nmsocket_cleanup(&sock->children[i],
 						 false FLARG_PASS);
 			}

lib/isc/netmgr/tcp.c

@@ -62,6 +62,8 @@ static isc_result_t
 tcp_send_direct(isc_nmsocket_t *sock, isc__nm_uvreq_t *req);
 static void
 tcp_connect_cb(uv_connect_t *uvreq, int status);
+static void
+tcp_stop_cb(uv_handle_t *handle);
 
 static void
 tcp_connection_cb(uv_stream_t *server, int status);
@@ -683,7 +685,20 @@ isc__nm_async_tcpstop(isc__networker_t *worker, isc__netievent_t *ev0) {
 	RUNTIME_CHECK(atomic_compare_exchange_strong(&sock->closing,
 						     &(bool){ false }, true));
 
-	tcp_close_direct(sock);
+	/*
+	 * The order of the close operation is important here, the uv_close()
+	 * gets scheduled in the reverse order, so we need to close the timer
+	 * last, so its gone by the time we destroy the socket
+	 */
+
+	/* 2. close the listening socket */
+	isc__nmsocket_clearcb(sock);
+	isc__nm_stop_reading(sock);
+	uv_close(&sock->uv_handle.handle, tcp_stop_cb);
+
+	/* 1. close the read timer */
+	isc__nmsocket_timer_stop(sock);
+	uv_close(&sock->read_timer, NULL);
 
 	(void)atomic_fetch_sub(&sock->parent->rchildren, 1);
 
@@ -1217,25 +1232,12 @@ tcp_close_cb(uv_handle_t *handle) {
 	tcp_close_sock(sock);
 }
 
-static void
-read_timer_close_cb(uv_handle_t *handle) {
-	isc_nmsocket_t *sock = uv_handle_get_data(handle);
-	uv_handle_set_data(handle, NULL);
-
-	if (sock->parent) {
-		uv_close(&sock->uv_handle.handle, tcp_stop_cb);
-	} else if (uv_is_closing(&sock->uv_handle.handle)) {
-		tcp_close_sock(sock);
-	} else {
-		uv_close(&sock->uv_handle.handle, tcp_close_cb);
-	}
-}
-
 static void
 tcp_close_direct(isc_nmsocket_t *sock) {
 	REQUIRE(VALID_NMSOCK(sock));
 	REQUIRE(sock->tid == isc_tid());
 	REQUIRE(atomic_load(&sock->closing));
+	REQUIRE(sock->parent == NULL);
 
 	if (sock->server != NULL) {
 		REQUIRE(VALID_NMSOCK(sock->server));
@@ -1251,12 +1253,31 @@ tcp_close_direct(isc_nmsocket_t *sock) {
 		isc_quota_detach(&sock->quota);
 	}
 
-	isc__nmsocket_clearcb(sock);
-	isc__nmsocket_timer_stop(sock);
-	isc__nm_stop_reading(sock);
+	/*
+	 * The order of the close operation is important here, the uv_close()
+	 * gets scheduled in the reverse order, so we need to close the timer
+	 * last, so its gone by the time we destroy the socket
+	 */
 
+	if (!uv_is_closing(&sock->uv_handle.handle)) {
+		/* Normal order of operation */
+
+		/* 2. close the socket + destroy the socket in callback */
+		isc__nmsocket_clearcb(sock);
+		isc__nm_stop_reading(sock);
+		uv_close(&sock->uv_handle.handle, tcp_close_cb);
+
+		/* 1. close the timer */
+		isc__nmsocket_timer_stop(sock);
+		uv_close((uv_handle_t *)&sock->read_timer, NULL);
+	} else {
+		/* The socket was already closed elsewhere */
+
+		/* 1. close the timer + destroy the socket in callback */
+		isc__nmsocket_timer_stop(sock);
 		uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
-	uv_close((uv_handle_t *)&sock->read_timer, read_timer_close_cb);
+		uv_close((uv_handle_t *)&sock->read_timer, tcp_close_cb);
+	}
 }
 
 void

lib/isc/netmgr/tcpdns.c

@@ -63,6 +63,9 @@ tcpdns_connect_cb(uv_connect_t *uvreq, int status);
 static void
 tcpdns_connection_cb(uv_stream_t *server, int status);
 
+static void
+tcpdns_stop_cb(uv_handle_t *handle);
+
 static void
 tcpdns_close_cb(uv_handle_t *uvhandle);
 
@@ -646,7 +649,20 @@ isc__nm_async_tcpdnsstop(isc__networker_t *worker, isc__netievent_t *ev0) {
 	RUNTIME_CHECK(atomic_compare_exchange_strong(&sock->closing,
 						     &(bool){ false }, true));
 
-	tcpdns_close_direct(sock);
+	/*
+	 * The order of the close operation is important here, the uv_close()
+	 * gets scheduled in the reverse order, so we need to close the timer
+	 * last, so its gone by the time we destroy the socket
+	 */
+
+	/* 2. close the listening socket */
+	isc__nmsocket_clearcb(sock);
+	isc__nm_stop_reading(sock);
+	uv_close(&sock->uv_handle.handle, tcpdns_stop_cb);
+
+	/* 1. close the read timer */
+	isc__nmsocket_timer_stop(sock);
+	uv_close(&sock->read_timer, NULL);
 
 	(void)atomic_fetch_sub(&sock->parent->rchildren, 1);
 
@@ -1270,22 +1286,6 @@ tcpdns_close_cb(uv_handle_t *handle) {
 	tcpdns_close_sock(sock);
 }
 
-static void
-read_timer_close_cb(uv_handle_t *timer) {
-	isc_nmsocket_t *sock = uv_handle_get_data(timer);
-	uv_handle_set_data(timer, NULL);
-
-	REQUIRE(VALID_NMSOCK(sock));
-
-	if (sock->parent) {
-		uv_close(&sock->uv_handle.handle, tcpdns_stop_cb);
-	} else if (uv_is_closing(&sock->uv_handle.handle)) {
-		tcpdns_close_sock(sock);
-	} else {
-		uv_close(&sock->uv_handle.handle, tcpdns_close_cb);
-	}
-}
-
 static void
 tcpdns_close_direct(isc_nmsocket_t *sock) {
 	REQUIRE(VALID_NMSOCK(sock));
@@ -1300,12 +1300,30 @@ tcpdns_close_direct(isc_nmsocket_t *sock) {
 		isc_nmhandle_detach(&sock->recv_handle);
 	}
 
-	isc__nmsocket_clearcb(sock);
-	isc__nmsocket_timer_stop(sock);
-	isc__nm_stop_reading(sock);
+	/*
+	 * The order of the close operation is important here, the uv_close()
+	 * gets scheduled in the reverse order, so we need to close the timer
+	 * last, so its gone by the time we destroy the socket
+	 */
 
+	if (!uv_is_closing(&sock->uv_handle.handle)) {
+		/* Normal order of operation */
+
+		/* 2. close the socket + destroy the socket in callback */
+		isc__nmsocket_clearcb(sock);
+		isc__nm_stop_reading(sock);
+		uv_close(&sock->uv_handle.handle, tcpdns_close_cb);
+
+		/* 1. close the timer */
+		uv_close((uv_handle_t *)&sock->read_timer, NULL);
+	} else {
+		/* The socket was already closed elsewhere */
+
+		/* 1. close the timer + destroy the socket in callback */
+		isc__nmsocket_timer_stop(sock);
 		uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
-	uv_close((uv_handle_t *)&sock->read_timer, read_timer_close_cb);
+		uv_close((uv_handle_t *)&sock->read_timer, tcpdns_close_cb);
+	}
 }
 
 void

lib/isc/netmgr/tlsdns.c

@@ -56,6 +56,9 @@ tlsdns_connect_cb(uv_connect_t *uvreq, int status);
 static void
 tlsdns_connection_cb(uv_stream_t *server, int status);
 
+static void
+tlsdns_stop_cb(uv_handle_t *handle);
+
 static void
 tlsdns_close_cb(uv_handle_t *uvhandle);
 
@@ -769,7 +772,20 @@ isc__nm_async_tlsdnsstop(isc__networker_t *worker, isc__netievent_t *ev0) {
 	RUNTIME_CHECK(atomic_compare_exchange_strong(&sock->closing,
 						     &(bool){ false }, true));
 
-	tlsdns_close_direct(sock);
+	/*
+	 * The order of the close operation is important here, the uv_close()
+	 * gets scheduled in the reverse order, so we need to close the timer
+	 * last, so its gone by the time we destroy the socket
+	 */
+
+	/* 2. close the listening socket */
+	isc__nmsocket_clearcb(sock);
+	isc__nm_stop_reading(sock);
+	uv_close(&sock->uv_handle.handle, tlsdns_stop_cb);
+
+	/* 1. close the read timer */
+	isc__nmsocket_timer_stop(sock);
+	uv_close(&sock->read_timer, NULL);
 
 	(void)atomic_fetch_sub(&sock->parent->rchildren, 1);
 
@@ -1908,27 +1924,12 @@ tlsdns_close_cb(uv_handle_t *handle) {
 	tlsdns_close_sock(sock);
 }
 
-static void
-read_timer_close_cb(uv_handle_t *handle) {
-	isc_nmsocket_t *sock = uv_handle_get_data(handle);
-	uv_handle_set_data(handle, NULL);
-
-	REQUIRE(VALID_NMSOCK(sock));
-
-	if (sock->parent) {
-		uv_close(&sock->uv_handle.handle, tlsdns_stop_cb);
-	} else if (uv_is_closing(&sock->uv_handle.handle)) {
-		tlsdns_close_sock(sock);
-	} else {
-		uv_close(&sock->uv_handle.handle, tlsdns_close_cb);
-	}
-}
-
 static void
 tlsdns_close_direct(isc_nmsocket_t *sock) {
 	REQUIRE(VALID_NMSOCK(sock));
 	REQUIRE(sock->tid == isc_tid());
 	REQUIRE(atomic_load(&sock->closing));
+	REQUIRE(sock->parent == NULL);
 
 	REQUIRE(sock->tls.pending_req == NULL);
 
@@ -1940,12 +1941,31 @@ tlsdns_close_direct(isc_nmsocket_t *sock) {
 		isc_nmhandle_detach(&sock->recv_handle);
 	}
 
-	isc__nmsocket_clearcb(sock);
-	isc__nmsocket_timer_stop(sock);
-	isc__nm_stop_reading(sock);
+	/*
+	 * The order of the close operation is important here, the uv_close()
+	 * gets scheduled in the reverse order, so we need to close the timer
+	 * last, so its gone by the time we destroy the socket
+	 */
 
+	if (!uv_is_closing(&sock->uv_handle.handle)) {
+		/* Normal order of operation */
+
+		/* 2. close the socket + destroy the socket in callback */
+		isc__nmsocket_clearcb(sock);
+		isc__nm_stop_reading(sock);
+		uv_close(&sock->uv_handle.handle, tlsdns_close_cb);
+
+		/* 1. close the timer */
+		isc__nmsocket_timer_stop(sock);
+		uv_close((uv_handle_t *)&sock->read_timer, NULL);
+	} else {
+		/* The socket was already closed elsewhere */
+
+		/* 1. close the timer + destroy the socket in callback */
+		isc__nmsocket_timer_stop(sock);
 		uv_handle_set_data((uv_handle_t *)&sock->read_timer, sock);
-	uv_close((uv_handle_t *)&sock->read_timer, read_timer_close_cb);
+		uv_close((uv_handle_t *)&sock->read_timer, tlsdns_close_cb);
+	}
 }
 
 void

lib/isc/netmgr/udp.c

@@ -65,9 +65,6 @@ udp_send_cb(uv_udp_send_t *req, int status);
 static void
 udp_close_cb(uv_handle_t *handle);
 
-static void
-read_timer_close_cb(uv_handle_t *handle);
-
 static uv_os_sock_t
 isc__nm_udp_lb_socket(isc_nm_t *mgr, sa_family_t sa_family) {
 	isc_result_t result;
@@ -1008,14 +1005,6 @@ udp_close_cb(uv_handle_t *handle) {
 	}
 }
 
-static void
-read_timer_close_cb(uv_handle_t *handle) {
-	isc_nmsocket_t *sock = uv_handle_get_data(handle);
-	uv_handle_set_data(handle, NULL);
-
-	uv_close(&sock->uv_handle.handle, udp_close_cb);
-}
-
 void
 isc__nm_udp_close(isc_nmsocket_t *sock) {
 	REQUIRE(VALID_NMSOCK(sock));
@@ -1031,7 +1020,20 @@ isc__nm_udp_close(isc_nmsocket_t *sock) {
 	isc__nmsocket_timer_stop(sock);
 	isc__nm_stop_reading(sock);
 
-	uv_close((uv_handle_t *)&sock->read_timer, read_timer_close_cb);
+	/*
+	 * The order of the close operation is important here, the uv_close()
+	 * gets scheduled in the reverse order, so we need to close the timer
+	 * last, so its gone by the time we destroy the socket
+	 */
+
+	/* 2. close the listening socket */
+	isc__nmsocket_clearcb(sock);
+	isc__nm_stop_reading(sock);
+	uv_close(&sock->uv_handle.handle, udp_close_cb);
+
+	/* 1. close the read timer */
+	isc__nmsocket_timer_stop(sock);
+	uv_close((uv_handle_t *)&sock->read_timer, NULL);
 }
 
 void