unix: Postpone restore_sk_common() of standalone sockets

restore_sk_common() may shutdown a socket, and queuer
won't be able to connect to it. So, this action must
be postponed.

We have this problem since long ago, but we are lucky
we haven't bumped in it.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/sk-unix.c

@@ -806,8 +806,14 @@ struct unix_sk_info {
 	 * that should do the queueing.
 	 */
 	struct unix_sk_info *queuer;
+	/*
+	 * These bits are set by task-owner of this unix_sk_info.
+	 * Another tasks can only read them.
+	 */
 	u8 bound:1;
 	u8 listen:1;
+	u8 is_connected:1;
+	u8 peer_queue_restored:1; /* Set in 1 after we restore peer's queue */
 };
 
 struct scm_fle {
@@ -985,6 +991,20 @@ static bool peer_is_not_prepared(struct unix_sk_info *peer)
 		return (!peer->listen);
 }
 
+static int restore_unix_queue(int fd, struct unix_sk_info *peer)
+{
+	struct pstree_item *task;
+
+	if (restore_sk_queue(fd, peer->ue->id))
+		return -1;
+	if (peer->queuer)
+		peer->queuer->peer_queue_restored = true;
+
+	task = file_master(&peer->d)->task;
+	set_fds_event(vpid(task));
+	return 0;
+}
+
 static int shutdown_unix_sk(int sk, struct unix_sk_info *ui)
 {
 	int how;
@@ -1100,7 +1120,8 @@ static int post_open_standalone(struct file_desc *d, int fd)
 			(ui->ue->uflags & (USK_CALLBACK | USK_INHERIT)));
 
 	peer = ui->peer;
-	BUG_ON(peer == NULL);
+	if (!peer || ui->is_connected)
+		goto restore_sk_common;
 
 	/* Skip external sockets */
 	if (!list_empty(&peer->d.fd_info_head))
@@ -1123,12 +1144,17 @@ static int post_open_standalone(struct file_desc *d, int fd)
 		revert_unix_sk_cwd(&cwd_fd, &root_fd);
 		return -1;
 	}
+	ui->is_connected = true;
 
 	revert_unix_sk_cwd(&cwd_fd, &root_fd);
 
-	if (peer->queuer == ui && restore_sk_queue(fd, peer->ue->id))
+	if (peer->queuer == ui &&
+	    !(peer->ue->uflags & USK_EXTERN) &&
+	    restore_unix_queue(fd, peer))
 		return -1;
-
+restore_sk_common:
+	if (ui->queuer && !ui->queuer->peer_queue_restored)
+		return 1;
 	return restore_sk_common(fd, ui);
 }
 
@@ -1256,10 +1282,10 @@ static int post_open_interconnected_master(struct unix_sk_info *ui)
 	fle_peer = file_master(&peer->d);
 	BUG_ON(fle->task != fle_peer->task); /* See interconnected_pair() */
 
-	if (restore_sk_queue(fle->fe->fd, peer->ue->id))
+	if (restore_unix_queue(fle->fe->fd, peer))
 		return -1;
 
-	if (restore_sk_queue(fle_peer->fe->fd, ui->ue->id))
+	if (restore_unix_queue(fle_peer->fe->fd, ui))
 		return -1;
 
 	if (restore_sk_common(fle->fe->fd, ui))
@@ -1395,7 +1421,7 @@ static int open_unixsk_standalone(struct unix_sk_info *ui, int *new_fd)
 		 * Restore queue at the one end,
 		 * before closing the second one.
 		 */
-		if (restore_sk_queue(sks[1], ui->ue->id)) {
+		if (restore_unix_queue(sks[1], ui)) {
 			pr_perror("Can't restore socket queue");
 			return -1;
 		}
@@ -1431,7 +1457,7 @@ static int open_unixsk_standalone(struct unix_sk_info *ui, int *new_fd)
 		 * This must be after the connect() hack, because
 		 * connect() flushes receive queue.
 		 */
-		if (restore_sk_queue(sks[1], ui->ue->id)) {
+		if (restore_unix_queue(sks[1], ui)) {
 			pr_perror("Can't restore socket queue");
 			return -1;
 		}
@@ -1475,11 +1501,13 @@ static int open_unixsk_standalone(struct unix_sk_info *ui, int *new_fd)
 		wake_connected_sockets(ui);
 	}
 
-	if (ui->peer) {
+	if (ui->peer || ui->queuer) {
 		/*
-		 * We need to connect() to the peer, but the
+		 * 1)We need to connect() to the peer, but the
 		 * guy might have not bind()-ed himself, so
 		 * let's postpone this.
+		 * 2)Queuer won't be able to connect, if we do
+		 * shutdown, so postpone it.
 		 */
 		*new_fd = sk;
 		return 1;
@@ -1602,6 +1630,8 @@ static int collect_one_unixsk(void *o, ProtobufCMessage *base, struct cr_img *i)
 	ui->peer = NULL;
 	ui->bound = 0;
 	ui->listen = 0;
+	ui->is_connected = 0;
+	ui->peer_queue_restored = 0;
 	INIT_LIST_HEAD(&ui->connected);
 	INIT_LIST_HEAD(&ui->node);
 	INIT_LIST_HEAD(&ui->scm_fles);