[PATCH v3] vhost: fix connect hang in client mode

[Ilya Maximets <i.maximets@samsung.com>]

If something abnormal happened to QEMU, 'connect()' can block calling
thread (e.g. main thread of OVS) forever or for a really long time.
This can break whole application or block the reconnection thread.

Example with OVS:

	ovs_rcu(urcu2)|WARN|blocked 512000 ms waiting for main to quiesce
	(gdb) bt
	#0  connect () from /lib64/libpthread.so.0
	#1  vhost_user_create_client (vsocket=0xa816e0)
	#2  rte_vhost_driver_register
	#3  netdev_dpdk_vhost_user_construct
	#4  netdev_open (name=0xa664b0 "vhost1")
	[...]
	#11 main

Fix that by setting non-blocking mode for client sockets for connection.

Fixes: 64ab701c3d1e ("vhost: add vhost-user client mode")

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
---
This was reproduced with current QEMU master branch
(commit 1ecfb24da987b862f) + patch-set "vhost-user reconnect fixes"
(https://lists.nongnu.org/archive/html/qemu-devel/2016-07/msg01547.html).

OVS was patched to support client mode:
http://openvswitch.org/pipermail/dev/2016-July/074972.html

Following script forces QEMU to fail to initialize vhost because
disconnection occures while device not fully configured:

	while true
	do
		ovs-vsctl set Interface vhost1 ofport_request=125
		ovs-vsctl set Interface vhost1 ofport_request=126
	done

As a result: QEMU still works, network interface broken and OVS main
             thread stalled inside 'connect()'.

Version 3:
	* Removed unnecessary 'getsockopt()' check.

Version 2:
	* EINPROGRESS not checked. EISCONN checked instead on
	  the next iteration of reconnection loop.



 lib/librte_vhost/vhost_user/vhost-net-user.c | 52 +++++++++++++++++++++++++---
 1 file changed, 48 insertions(+), 4 deletions(-)

diff --git a/lib/librte_vhost/vhost_user/vhost-net-user.c b/lib/librte_vhost/vhost_user/vhost-net-user.c
index 62c5ec3..b35594d 100644
--- a/lib/librte_vhost/vhost_user/vhost-net-user.c
+++ b/lib/librte_vhost/vhost_user/vhost-net-user.c
@@ -43,6 +43,7 @@
 #include <sys/un.h>
 #include <sys/queue.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <pthread.h>
 
 #include <rte_log.h>
@@ -449,6 +450,14 @@ create_unix_socket(const char *path, struct sockaddr_un *un, bool is_server)
 	RTE_LOG(INFO, VHOST_CONFIG, "vhost-user %s: socket created, fd: %d\n",
 		is_server ? "server" : "client", fd);
 
+	if (!is_server && fcntl(fd, F_SETFL, O_NONBLOCK)) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"vhost-user: can't set nonblocking mode for socket, fd: "
+			"%d (%s)\n", fd, strerror(errno));
+		close(fd);
+		return -1;
+	}
+
 	memset(un, 0, sizeof(*un));
 	un->sun_family = AF_UNIX;
 	strncpy(un->sun_path, path, sizeof(un->sun_path));
@@ -516,9 +525,33 @@ struct vhost_user_reconnect_list {
 static struct vhost_user_reconnect_list reconn_list;
 static pthread_t reconn_tid;
 
+static int
+vhost_user_connect_nonblock(int fd, struct sockaddr *un, size_t sz)
+{
+	int ret, flags;
+
+	ret = connect(fd, un, sz);
+	if (ret < 0 && errno != EISCONN)
+		return -1;
+
+	flags = fcntl(fd, F_GETFL, 0);
+	if (flags < 0) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+			"can't get flags for connfd %d\n", fd);
+		return -2;
+	}
+	if ((flags & O_NONBLOCK) && fcntl(fd, F_SETFL, flags & ~O_NONBLOCK)) {
+		RTE_LOG(ERR, VHOST_CONFIG,
+				"can't disable nonblocking on fd %d\n", fd);
+		return -2;
+	}
+	return 0;
+}
+
 static void *
 vhost_user_client_reconnect(void *arg __rte_unused)
 {
+	int ret;
 	struct vhost_user_reconnect *reconn, *next;
 
 	while (1) {
@@ -532,13 +565,23 @@ vhost_user_client_reconnect(void *arg __rte_unused)
 		     reconn != NULL; reconn = next) {
 			next = TAILQ_NEXT(reconn, next);
 
-			if (connect(reconn->fd, (struct sockaddr *)&reconn->un,
-				    sizeof(reconn->un)) < 0)
+			ret = vhost_user_connect_nonblock(reconn->fd,
+						(struct sockaddr *)&reconn->un,
+						sizeof(reconn->un));
+			if (ret == -2) {
+				close(reconn->fd);
+				RTE_LOG(ERR, VHOST_CONFIG,
+					"reconnection for fd %d failed\n",
+					reconn->fd);
+				goto remove_fd;
+			}
+			if (ret == -1)
 				continue;
 
 			RTE_LOG(INFO, VHOST_CONFIG,
 				"%s: connected\n", reconn->vsocket->path);
 			vhost_user_add_connection(reconn->fd, reconn->vsocket);
+remove_fd:
 			TAILQ_REMOVE(&reconn_list.head, reconn, next);
 			free(reconn);
 		}
@@ -579,7 +622,8 @@ vhost_user_create_client(struct vhost_user_socket *vsocket)
 	if (fd < 0)
 		return -1;
 
-	ret = connect(fd, (struct sockaddr *)&un, sizeof(un));
+	ret = vhost_user_connect_nonblock(fd, (struct sockaddr *)&un,
+					  sizeof(un));
 	if (ret == 0) {
 		vhost_user_add_connection(fd, vsocket);
 		return 0;
@@ -589,7 +633,7 @@ vhost_user_create_client(struct vhost_user_socket *vsocket)
 		"failed to connect to %s: %s\n",
 		path, strerror(errno));
 
-	if (!vsocket->reconnect) {
+	if (ret == -2 || !vsocket->reconnect) {
 		close(fd);
 		return -1;
 	}
-- 
2.7.4