Remove getaddrinfo in SendDummyPacket() to address malloc deadlock

`SendDummyPacket` eventually calls `getaddrinfo` (which is a reentrant),
however, `getaddrinfo` is not an async-signal-safe function.
`getaddrinfo` internally calls `malloc`, which is strongly advised to
not do within a signal handler as it may cause deadlocks.
Cache the accepted socket information for the listener, so that it can
be reused in `SendDummyPacket()`.

The purpose of `SendDummyPacket` is to exit more quickly; it
circumvents the polling that happens, which eventually times out after 250ms.

Without `SendDummyPacket()`, there will be multiple test failures since
some tests expects the backend connection to terminate almost
immediately.

To view all the async-signal-safe functions, please view
the signal-safety(7) — Linux manual page.

Reviewed-by: Soumyadeep Chakraborty <soumyadeep2007@gmail.com>
Reviewed-by: Andrew Repp <reppa@vmware.com>

Author: Chibin

contrib/interconnect/udp/ic_udpifc.c

@@ -640,6 +640,9 @@ typedef struct ICStatistics
 /* Statistics for UDP interconnect. */
 static ICStatistics ic_statistics;
 
+static struct addrinfo udp_dummy_packet_addrinfo;
+static struct sockaddr udp_dummy_packet_sockaddr;
+
 /* UDP listen fd */
 int			UDP_listenerFd;
 
@@ -669,7 +672,8 @@ static void SendDummyPacket(void);
 
 static void getSockAddr(struct sockaddr_storage *peer, socklen_t *peer_len, const char *listenerAddr, int listenerPort);
 static uint32 setUDPSocketBufferSize(int ic_socket, int buffer_type);
-static void setupUDPListeningSocket(int *listenerSocketFd, int32 *listenerPort, int *txFamily);
+static void setupUDPListeningSocket(int *listenerSocketFd, int32 *listenerPort,
+							int *txFamily, struct addrinfo *listenerAddrinfo, struct sockaddr *listenerSockaddr);
 static ChunkTransportStateEntry *startOutgoingUDPConnections(ChunkTransportState *transportStates,
 							ExecSlice *sendSlice,
 							int *pOutgoingCount);
@@ -1157,13 +1161,12 @@ resetRxThreadError()
 	pg_atomic_write_u32(&ic_control_info.eno, 0);
 }
 
-
 /*
  * setupUDPListeningSocket
  * 		Setup udp listening socket.
  */
 static void
-setupUDPListeningSocket(int *listenerSocketFd, int32 *listenerPort, int *txFamily)
+setupUDPListeningSocket(int *listenerSocketFd, int32 *listenerPort, int *txFamily, struct addrinfo *listenerAddrinfo, struct sockaddr *listenerSockaddr)
 {
 	struct addrinfo 		*addrs = NULL;
 	struct addrinfo 		*addr;
@@ -1284,6 +1287,16 @@ setupUDPListeningSocket(int *listenerSocketFd, int32 *listenerPort, int *txFamil
 	if (!addr || ic_socket == PGINVALID_SOCKET)
 		goto startup_failed;
 
+	/*
+	 * cache the successful addrinfo and sockaddr of the listening socket, so
+	 * we can use this information to connect to the listening socket.
+	 */
+	if (listenerAddrinfo != NULL && listenerSockaddr != NULL )
+	{
+		memcpy(listenerAddrinfo, addr, sizeof(udp_dummy_packet_addrinfo));
+		memcpy(listenerSockaddr, addr->ai_addr, sizeof(udp_dummy_packet_sockaddr));
+	}
+
 	/* Memorize the socket fd, kernel assigned port and address family */
 	*listenerSocketFd = ic_socket;
 	if (listenerAddr.ss_family == AF_INET6)
@@ -1429,8 +1442,9 @@ InitMotionUDPIFC(int *listenerSocketFd, int32 *listenerPort)
 	/*
 	 * setup listening socket and sending socket for Interconnect.
 	 */
-	setupUDPListeningSocket(listenerSocketFd, listenerPort, &txFamily);
-	setupUDPListeningSocket(&ICSenderSocket, &ICSenderPort, &ICSenderFamily);
+	setupUDPListeningSocket(listenerSocketFd, listenerPort, &txFamily,
+			&udp_dummy_packet_addrinfo, &udp_dummy_packet_sockaddr);
+	setupUDPListeningSocket(&ICSenderSocket, &ICSenderPort, &ICSenderFamily, NULL, NULL);
 
 	/* Initialize receive control data. */
 	resetMainThreadWaiting(&rx_control_info.mainWaitingState);
@@ -1538,6 +1552,9 @@ static inline void CleanupMotionUDPIFC(void)
 	ICSenderPort = 0;
 	ICSenderFamily = 0;
 
+	memset(&udp_dummy_packet_addrinfo, 0, sizeof(udp_dummy_packet_addrinfo));
+	memset(&udp_dummy_packet_sockaddr, 0, sizeof(udp_dummy_packet_sockaddr));
+
 #ifdef USE_ASSERT_CHECKING
 
 	/*
@@ -7226,104 +7243,50 @@ WaitInterconnectQuitUDPIFC(void)
 static void
 SendDummyPacket(void)
 {
-	int			sockfd = -1;
-	int			ret;
-	struct addrinfo *addrs = NULL;
-	struct addrinfo *rp;
-	struct addrinfo hint;
-	uint16		udp_listener;
-	char		port_str[32] = {0};
-	char	   *dummy_pkt = "stop it";
-	int			counter;
-
+	int					ret;
+	in_port_t			udp_listener_port;
+	char				*dummy_pkt = "stop it";
+	int					counter;
+	struct sockaddr_in	*addr_in = NULL;
+	struct sockaddr_in	dest_addr;
 	/*
 	 * Get address info from interconnect udp listener port
 	 */
-	udp_listener = GetListenPortUDP();
-	snprintf(port_str, sizeof(port_str), "%d", udp_listener);
-
-	MemSet(&hint, 0, sizeof(hint));
-	hint.ai_socktype = SOCK_DGRAM;
-	hint.ai_family = AF_UNSPEC; /* Allow for IPv4 or IPv6  */
-
-	/* Never do name resolution */
-#ifdef AI_NUMERICSERV
-	hint.ai_flags = AI_NUMERICHOST | AI_NUMERICSERV;
-#else
-	hint.ai_flags = AI_NUMERICHOST;
-#endif
-
-	ret = pg_getaddrinfo_all(interconnect_address, port_str, &hint, &addrs);
-	if (ret || !addrs)
-	{
-		elog(LOG, "send dummy packet failed, pg_getaddrinfo_all(): %m");
-		goto send_error;
-	}
-
-	for (rp = addrs; rp != NULL; rp = rp->ai_next)
-	{
-		/* Create socket according to pg_getaddrinfo_all() */
-		sockfd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
-		if (sockfd < 0)
-			continue;
+	udp_listener_port = (Gp_listener_port >> 16) & 0x0ffff;
 
-		if (!pg_set_noblock(sockfd))
-		{
-			if (sockfd >= 0)
-			{
-				closesocket(sockfd);
-				sockfd = -1;
-			}
-			continue;
-		}
-		break;
-	}
-
-	if (rp == NULL)
-	{
-		elog(LOG, "send dummy packet failed, create socket failed: %m");
-		goto send_error;
-	}
+	addr_in = (struct sockaddr_in *) &udp_dummy_packet_sockaddr;
+	memset(&dest_addr, 0, sizeof(dest_addr));
+	dest_addr.sin_family = addr_in->sin_family;
+	dest_addr.sin_port = htons(udp_listener_port);
+	dest_addr.sin_addr.s_addr = addr_in->sin_addr.s_addr;
 
 	/*
-	 * Send a dummy package to the interconnect listener, try 10 times
+	 * Send a dummy package to the interconnect listener, try 10 times.
+	 * We don't want to close the socket at the end of this function, since
+	 * the socket will eventually close during the motion layer cleanup.
 	 */
-
 	counter = 0;
 	while (counter < 10)
 	{
 		counter++;
-		ret = sendto(sockfd, dummy_pkt, strlen(dummy_pkt), 0, rp->ai_addr, rp->ai_addrlen);
+		ret = sendto(ICSenderSocket, dummy_pkt, strlen(dummy_pkt), 0, (struct sockaddr *) &dest_addr, sizeof(dest_addr));
 		if (ret < 0)
 		{
 			if (errno == EINTR || errno == EAGAIN || errno == EWOULDBLOCK)
 				continue;
 			else
 			{
 				elog(LOG, "send dummy packet failed, sendto failed: %m");
-				goto send_error;
+				return;
 			}
 		}
 		break;
 	}
 
 	if (counter >= 10)
 	{
-		elog(LOG, "send dummy packet failed, sendto failed: %m");
-		goto send_error;
+		elog(LOG, "send dummy packet failed, sendto failed with 10 times: %m");
 	}
-
-	pg_freeaddrinfo_all(hint.ai_family, addrs);
-	closesocket(sockfd);
-	return;
-
-send_error:
-
-	if (addrs)
-		pg_freeaddrinfo_all(hint.ai_family, addrs);
-	if (sockfd != -1)
-		closesocket(sockfd);
-	return;
 }
 
 void logChunkParseDetails(MotionConn *conn, uint32 ic_instance_id)