From 6ed36cd6e36e9bd15ae4ca39f5b8163c4740c484 Mon Sep 17 00:00:00 2001
From: Olivier Fourdan <ofourdan@redhat.com>
Date: Tue, 25 Sep 2018 13:50:09 +0200
Subject: [PATCH] wayland: No xdg-output events without a logical monitor

To avoid a known race condition in the wl_output protocol documented in
https://phabricator.freedesktop.org/T7722, mutter delays the `wl_output`
destruction but nullify the `logical_monitor` associated with the
`wl_output` and the binding routine `bind_output()` makes sure not to
send wl_output events if the `logical_monitor` is `NULL` (see commit
1923db97).

The binding routine for `xdg_output` however does not check for such a
condition, hence if the output configuration changes while a client is
binding to xdg-output (typically Xwayland at startup), mutter would
crash while trying to access the `logical_monitor` which was nullified
by the change in configuration.

Just like `bind_output()` does for wl_output, do not send xdg-output
events if there is no `logical_monitor` yet.

Closes: https://gitlab.gnome.org/GNOME/mutter/issues/194

(cherry picked from commit 68ec9ac017157def9b7c25dd8141dc0e93d9f918)
---
 src/wayland/meta-wayland-outputs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/wayland/meta-wayland-outputs.c b/src/wayland/meta-wayland-outputs.c
index bc67b90be..1f99a163d 100644
--- a/src/wayland/meta-wayland-outputs.c
+++ b/src/wayland/meta-wayland-outputs.c
@@ -592,6 +592,9 @@ meta_xdg_output_manager_get_xdg_output (struct wl_client   *client,
   wayland_output->xdg_output_resources =
     g_list_prepend (wayland_output->xdg_output_resources, xdg_output_resource);
 
+  if (!wayland_output->logical_monitor)
+    return;
+
   send_xdg_output_events (xdg_output_resource,
                           wayland_output,
                           wayland_output->logical_monitor,
-- 
2.19.0