If gnome-shell is started directly (instead of through gnome-session), it might deadlock with no output to the screen

[Yao Wei]

[ Impact ]

If gnome-shell is launched directly instead of launched through gnome-session, the process spawning `ibus-daemon` might cause deadlock and unable to start the graphics.

Since `ibusManager.js` checks whether service `org.freedesktop.IBus.session.GNOME.service` exists. In our case with Ubuntu ubiquity, we've turned off `gnome-session.service` so that the check failed and gnome-shell spawns `ibus-daemon` after the check.

[ Test case ]

 - In a terminal launch
 - env XDG_RUNTIME_DIR=/tmp/nested-runtime \
   dbus-run-session gnome-shell --nested --wayland
 - The shell should start without hanging
 - Repeat this multiple times and ensure it works reliably

[ Regression potential ]

- Shell (and or its extensions) may not be able to spawn child processes
- Applications launched by the shell may inherit the rlimits of mutter

---

I tried using gdb to gnome-shell and discovered it's hanging in a child process spawning `ibus-daemon`, but is still in child_setup of `Glib.spawn_async` function:

```
root@dell-desktop:/home/oem# cat /tmp/log
== Stack trace for context 0x5584da793180 ==
#0 5584dbd2d478 i resource:///org/gnome/shell/misc/ibusManager.js:119 (2776aa47bfb0 @ 12)
#1 5584dbd2d3a8 i resource:///org/gnome/shell/misc/ibusManager.js:114 (2776aa47bf60 @ 426)
#2 5584dbd2d308 i resource:///org/gnome/shell/misc/ibusManager.js:90 (2776aa47bec0 @ 162)
#3 5584dbd2d268 i self-hosted:689 (34e3dc212650 @ 15)
```

which is, in ibusManager.js:

```
            const [success_, pid] = GLib.spawn_async(
                null, cmdLine, env,
                GLib.SpawnFlags.SEARCH_PATH | GLib.SpawnFlags.DO_NOT_REAP_CHILD,
                () => {
                    try {
                        global.context.restore_rlimit_nofile(); # <- here
                    } catch (err) {
                    }
                }
            );
```

Further code tracing found out that the deadlock is not during the execution of the function (`restore_rlimit_nofile`) but the access to the GObject (probably `global.context`).

Currently my propose to work around this issue is to add a 5 second `setTimeout` to the caller of `_spawn` function in `ibusManager.js`.

I've lost debugging information but I can try reproducing the issue and give the backtrace from gdb if needed.

[Marco Trevisan (Treviño) (3v1n0)]

This is handled via https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3293

[Launchpad Janitor (janitor)]

This bug was fixed in the package gnome-shell - 46.2-1ubuntu3

---------------
gnome-shell (46.2-1ubuntu3) oracular; urgency=medium

  * d/p/ubuntu-authd: Revert unwanted change causing ibus not to launch
    (LP: #2069381)

gnome-shell (46.2-1ubuntu2) oracular; urgency=medium

  * debian/patches/ubuntu-authd: Properly handle new-password messages requests
    (LP: #2068080)
  * d/p/ubuntu-authd: Add translatable js files to POTFILES.in (LP: #2068912)
  * d/p: Do not call unsafe functions when spawning new processes (LP: #2019776)
  * d/p: Resize tray icon windows to respect their actor representation
    (LP: #2012388)
  * d/p: Do not make tray icons to take any input event directly (LP: #2012388)
  * debian/patches/ubuntu-authd: Properly handle new-password messages requests
    (LP: #2068080)
  * d/p/ubuntu-authd: Add translatable js files to POTFILES.in (LP: #2068912)
  * d/p: Do not call unsafe functions when spawning new processes (LP: #2019776)
  * d/p: Resize tray icon windows to respect their actor representation
    (LP: #2012388)
  * d/p: Do not make tray icons to take any input event directly (LP: #2012388)

 -- Marco Trevisan (Treviño) <email address hidden> Fri, 14 Jun 2024 06:45:11 +0200