From 55812195ce3b77317e7a2dc642b78271f3a45c8e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Joan=20Bruguera=20Mic=C3=B3?= <joanbrugueram@gmail.com>
Date: Sat, 22 Jul 2023 01:20:58 +0000
Subject: [PATCH] module-rt: error out on load if no bus is available

Since the recent changes to the RT module in Pipewire 0.3.75, some
applications such as those using OpenAL-Soft crash on startup if
neither the session nor the system bus is available. For example:

    bwrap --dev-bind / / \
          --bind /dev/null /run/dbus/system_bus_socket \
          --bind /dev/null $XDG_RUNTIME_DIR/bus \
          openal-info

Will result in a crash with the following error message:

    dbus[1626147]: arguments to dbus_message_new_method_call() were
    incorrect, assertion "path != NULL" failed in file dbus-message.c
    line 1373.
    This is normally a bug in some application using the D-Bus library.

The RT module previously failed to load if no bus was available, but
after the recent changes, the init. logic runs in a thread, and failing
to obtain the bus no longer causes the module to fail to load.

Then, functions called later such as `pw_rtkit_make_realtime` assume
the bus is available and try to use it, causing the error above.

Put the logic for obtaining and checking the bus back to `module_init`,
so the module fails to load again if no bus is available.
---
 src/modules/module-rt.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/src/modules/module-rt.c b/src/modules/module-rt.c
index ebaffe7aa..7beca6a9f 100644
--- a/src/modules/module-rt.c
+++ b/src/modules/module-rt.c
@@ -923,14 +923,11 @@ static int check_rtkit(struct impl *impl, struct pw_context *context, bool *can_
 	return 0;
 }
 
-static int do_rtkit_setup(struct spa_loop *loop, bool async, uint32_t seq,
-		const void *data, size_t size, void *user_data)
+static int rtkit_get_bus(struct impl *impl)
 {
-	struct impl *impl = user_data;
 	int res;
-	long long retval;
 
-	pw_log_debug("enter rtkit setup");
+	pw_log_debug("enter rtkit get bus");
 
 	/* Checking xdg-desktop-portal. It works fine in all situations. */
 	if (impl->rtportal_enabled)
@@ -967,6 +964,18 @@ static int do_rtkit_setup(struct spa_loop *loop, bool async, uint32_t seq,
 			return res;
 		}
 	}
+
+	return 0;
+}
+
+static int do_rtkit_setup(struct spa_loop *loop, bool async, uint32_t seq,
+		const void *data, size_t size, void *user_data)
+{
+	struct impl *impl = user_data;
+	long long retval;
+
+	pw_log_debug("enter rtkit setup");
+
 	/* get some properties */
 	if (rtkit_get_int_property(impl, "MaxRealtimePriority", &retval) < 0) {
 		retval = 1;
@@ -1076,6 +1085,9 @@ int pipewire__module_init(struct pw_impl_module *module, const char *args)
 #ifdef HAVE_DBUS
 	impl->use_rtkit = use_rtkit;
 	if (impl->use_rtkit) {
+		if ((res = rtkit_get_bus(impl)) < 0)
+			goto error;
+
 		impl->thread_loop = pw_thread_loop_new("module-rt", NULL);
 		if (impl->thread_loop == NULL) {
 			res = -errno;