From 638dee44ec384a3409b8037e6143460986b56fac Mon Sep 17 00:00:00 2001
From: Michael Olbrich <m.olbrich@pengutronix.de>
Date: Mon, 20 Feb 2023 18:30:34 +0100
Subject: [PATCH] libweston: mitigate race when destroying outputs

With some displays connect, disconnect, connect events can happen is a very
short amount of time. When this happens, the output global may already be
destroyed when a client tries to bind it. As a result, the client is
disconnected with a protocol error. See [1] for more details on the general
problem.

To mitigate this problem call wl_global_remove() first and call
wl_global_destroy() several seconds later. This is inspired by the
implementation for the same problem in wlroots.

[1] https://gitlab.freedesktop.org/wayland/wayland/-/issues/10

Signed-off-by: Michael Olbrich <m.olbrich@pengutronix.de>
---
 libweston/compositor.c | 67 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 65 insertions(+), 2 deletions(-)

diff --git a/libweston/compositor.c b/libweston/compositor.c
index e0e71ac1..1ea730ac 100644
--- a/libweston/compositor.c
+++ b/libweston/compositor.c
@@ -5366,11 +5366,16 @@ bind_output(struct wl_client *client,
 		return;
 	}
 
+	if (!output) {
+		wl_resource_set_implementation(resource, &output_interface,
+					       NULL, NULL);
+		return;
+	}
+
 	wl_list_insert(&head->resource_list, wl_resource_get_link(resource));
 	wl_resource_set_implementation(resource, &output_interface, head,
 				       unbind_resource);
 
-	assert(output);
 	wl_output_send_geometry(resource,
 				output->x,
 				output->y,
@@ -5409,6 +5414,64 @@ weston_head_add_global(struct weston_head *head)
 					head, bind_output);
 }
 
+struct weston_destroy_global_data {
+	struct wl_global *global;
+	struct wl_event_source *event_source;
+	struct wl_listener destroy_listener;
+};
+
+static void
+weston_destroy_global(struct weston_destroy_global_data *data)
+{
+	wl_list_remove(&data->destroy_listener.link);
+	wl_global_destroy(data->global);
+	wl_event_source_remove(data->event_source);
+	free(data);
+}
+
+static void
+global_compositor_destroy_handler(struct wl_listener *listener, void *_data)
+{
+	struct weston_destroy_global_data *data =
+		wl_container_of(listener, data, destroy_listener);
+
+	weston_destroy_global(data);
+}
+
+static int
+weston_global_handle_timer_event(void *data)
+{
+	weston_destroy_global(data);
+	return 0;
+}
+
+static void
+weston_global_destroy_save(struct weston_compositor *compositor,
+			   struct wl_global *global)
+{
+	struct weston_destroy_global_data *data;
+	struct wl_event_loop *loop;
+
+	if (compositor->state == WESTON_COMPOSITOR_OFFSCREEN) {
+		wl_global_destroy(global);
+		return;
+	}
+
+	wl_global_remove(global);
+
+	data = xzalloc(sizeof *data);
+	data->global = global;
+
+	loop = wl_display_get_event_loop(compositor->wl_display);
+	data->event_source =
+		wl_event_loop_add_timer(loop, weston_global_handle_timer_event,
+					data);
+	wl_event_source_timer_update(data->event_source, 5000);
+
+	data->destroy_listener.notify = global_compositor_destroy_handler;
+	wl_signal_add(&compositor->destroy_signal, &data->destroy_listener);
+}
+
 /** Remove the global wl_output protocol object
  *
  * \param head The head whose global to remove.
@@ -5421,7 +5484,7 @@ weston_head_remove_global(struct weston_head *head)
 	struct wl_resource *resource, *tmp;
 
 	if (head->global)
-		wl_global_destroy(head->global);
+		weston_global_destroy_save(head->compositor, head->global);
 	head->global = NULL;
 
 	wl_resource_for_each_safe(resource, tmp, &head->resource_list) {