launcher-weston-launch: avoid race condition when switching VT merge

When using weston-launch launcher deactivating the VT is sometimes
racy and leads to Weston still being displayed. The launcher-direct.c
backend makes sure that the session signal is emitted first, then DRM
master is dropped and finally the VT switch is acknowledged via
VT_RELDISP.

However, in the weston-launch case the session signal is emitted via
a socket message to the weston process, which might get handled a bit
later. This leads to dropping DRM master and acknowledging the VT
switch prematurely.

Add a socket message which allows weston to notify weston-launch that
the signal has been emitted and deactivating can be proceeded.
Signed-off-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

libweston/launcher-weston-launch.c

@@ -201,7 +201,7 @@ static int
 launcher_weston_launch_data(int fd, uint32_t mask, void *data)
 {
 	struct launcher_weston_launch *launcher = data;
-	int len, ret;
+	int len, ret, reply;
 
 	if (mask & (WL_EVENT_HANGUP | WL_EVENT_ERROR)) {
 		weston_log("launcher socket closed, exiting\n");
@@ -226,6 +226,10 @@ launcher_weston_launch_data(int fd, uint32_t mask, void *data)
 		launcher->compositor->session_active = false;
 		wl_signal_emit(&launcher->compositor->session_signal,
 			       launcher->compositor);
+
+		reply = WESTON_LAUNCHER_DEACTIVATE_DONE;
+		launcher_weston_launch_send(launcher->fd, &reply, sizeof reply);
+
 		break;
 	default:
 		weston_log("unexpected event from weston-launch\n");

libweston/weston-launch.c

@@ -399,6 +399,22 @@ err0:
 	return 0;
 }
 
+static void
+close_input_fds(struct weston_launch *wl)
+{
+	struct stat s;
+	int fd;
+
+	for (fd = 3; fd <= wl->last_input_fd; fd++) {
+		if (fstat(fd, &s) == 0 && major(s.st_rdev) == INPUT_MAJOR) {
+			/* EVIOCREVOKE may fail if the kernel doesn't
+			 * support it, but all we can do is ignore it. */
+			ioctl(fd, EVIOCREVOKE, 0);
+			close(fd);
+		}
+	}
+}
+
 static int
 handle_socket_msg(struct weston_launch *wl)
 {
@@ -430,6 +446,11 @@ handle_socket_msg(struct weston_launch *wl)
 	case WESTON_LAUNCHER_OPEN:
 		ret = handle_open(wl, &msg, len);
 		break;
+	case WESTON_LAUNCHER_DEACTIVATE_DONE:
+		close_input_fds(wl);
+		drmDropMaster(wl->drm_fd);
+		ioctl(wl->tty, VT_RELDISP, 1);
+		break;
 	}
 
 	return ret;
@@ -490,22 +511,6 @@ quit(struct weston_launch *wl, int status)
 	exit(status);
 }
 
-static void
-close_input_fds(struct weston_launch *wl)
-{
-	struct stat s;
-	int fd;
-
-	for (fd = 3; fd <= wl->last_input_fd; fd++) {
-		if (fstat(fd, &s) == 0 && major(s.st_rdev) == INPUT_MAJOR) {
-			/* EVIOCREVOKE may fail if the kernel doesn't
-			 * support it, but all we can do is ignore it. */
-			ioctl(fd, EVIOCREVOKE, 0);
-			close(fd);
-		}
-	}
-}
-
 static int
 handle_signal(struct weston_launch *wl)
 {
@@ -551,9 +556,6 @@ handle_signal(struct weston_launch *wl)
 		break;
 	case SIGUSR1:
 		send_reply(wl, WESTON_LAUNCHER_DEACTIVATE);
-		close_input_fds(wl);
-		drmDropMaster(wl->drm_fd);
-		ioctl(wl->tty, VT_RELDISP, 1);
 		break;
 	case SIGUSR2:
 		ioctl(wl->tty, VT_RELDISP, VT_ACKACQ);

libweston/weston-launch.h

@@ -33,7 +33,8 @@ enum weston_launcher_opcode {
 enum weston_launcher_event {
 	WESTON_LAUNCHER_SUCCESS,
 	WESTON_LAUNCHER_ACTIVATE,
-	WESTON_LAUNCHER_DEACTIVATE
+	WESTON_LAUNCHER_DEACTIVATE,
+	WESTON_LAUNCHER_DEACTIVATE_DONE,
 };
 
 struct weston_launcher_message {