(In reply to Hussam Al-Tayeb from comment #0)
> Created attachment 331878 [details]
> coredump from user 120 (gdm)
> 
> Starting 3.21.4, gdm's gnome-shell instance crashes on systemctl stop gdm.
> 
> I'm back on gnome-3-20 branch for now so cannot get a good backtrace but I
> have attached the coredump.

Would need the debug symbols for gnome-shell, libmutter.so, libmutter-clutter.so and libmutter-cogl.so for that build to analyze that core dump.

Hello. I will get do a trunk build tonight with debug symbols the moment I finish working.
Thank you for investigating.

 coredumpctl gdb 6846
           PID: 6846 (gnome-shell)
           UID: 120 (gdm)
           GID: 120 (gdm)
        Signal: 11 (SEGV)
     Timestamp: Fri 2016-07-22 17:30:30 EEST (1min 45s ago)
  Command Line: /usr/bin/gnome-shell
    Executable: /usr/bin/gnome-shell
 Control Group: /user.slice/user-120.slice/session-c16.scope
          Unit: session-c16.scope
         Slice: user-120.slice
       Session: c16
     Owner UID: 120 (gdm)
       Boot ID: 140e278f6328472fa047ad0b82af5eec
    Machine ID: efb490e643e2436d9d1138df1745a008
      Hostname: hades
      Coredump: /var/lib/systemd/coredump/core.gnome-shell.120.140e278f6328472fa047ad0b82af5eec.6846.1469197830000000000000.lz4
       Message: Process 6846 (gnome-shell) of user 120 dumped core.
                
                Stack trace of thread 6846:
                #0  0x00007f12e69df8a0 meta_renderer_create_cogl_renderer (libmutter.so.0)
                #1  0x00007f12e5db8cd9 clutter_backend_do_real_create_context (libmutter-clutter-1.0.so)
                #2  0x00007f12e5dd1733 _clutter_feature_init (libmutter-clutter-1.0.so)
                #3  0x00007f12e5de2d59 clutter_init_real (libmutter-clutter-1.0.so)
                #4  0x00007f12e5de2ef0 post_parse_hook (libmutter-clutter-1.0.so)
                #5  0x00007f12e5296d37 g_option_context_parse (libglib-2.0.so.0)
                #6  0x00007f12e5de3c88 clutter_parse_args (libmutter-clutter-1.0.so)
                #7  0x00007f12e69d47b6 meta_clutter_init (libmutter.so.0)
                #8  0x00007f12e6a08e26 meta_init (libmutter.so.0)
                #9  0x0000000000401fa2 main (gnome-shell)
                #10 0x00007f12e4ca5741 __libc_start_main (libc.so.6)
                #11 0x0000000000402389 _start (gnome-shell)
                
                Stack trace of thread 6848:
                #0  0x00007f12e4d6330d poll (libc.so.6)
                #1  0x00007f12e528c196 n/a (libglib-2.0.so.0)
                #2  0x00007f12e528c2ac g_main_context_iteration (libglib-2.0.so.0)
                #3  0x00007f12e528c2f1 n/a (libglib-2.0.so.0)
                #4  0x00007f12e52b2715 n/a (libglib-2.0.so.0)
                #5  0x00007f12e502c434 start_thread (libpthread.so.0)
                #6  0x00007f12e4d6c30d __clone (libc.so.6)
                
                Stack trace of thread 6849:
                #0  0x00007f12e4d6330d poll (libc.so.6)
                #1  0x00007f12e528c196 n/a (libglib-2.0.so.0)
                #2  0x00007f12e528c522 g_main_loop_run (libglib-2.0.so.0)
                #3  0x00007f12e5877886 n/a (libgio-2.0.so.0)
                #4  0x00007f12e52b2715 n/a (libglib-2.0.so.0)
                #5  0x00007f12e502c434 start_thread (libpthread.so.0)
                #6  0x00007f12e4d6c30d __clone (libc.so.6)
                
                Stack trace of thread 6850:
                #0  0x00007f12e4d67e99 syscall (libc.so.6)
                #1  0x00007f12e52d06da g_cond_wait_until (libglib-2.0.so.0)
                #2  0x00007f12e5260ac9 n/a (libglib-2.0.so.0)
                #3  0x00007f12e52b30e6 n/a (libglib-2.0.so.0)
                #4  0x00007f12e52b2715 n/a (libglib-2.0.so.0)
                #5  0x00007f12e502c434 start_thread (libpthread.so.0)
                #6  0x00007f12e4d6c30d __clone (libc.so.6)

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Reading symbols from /usr/bin/gnome-shell...done.
[New LWP 6846]
[New LWP 6848]
[New LWP 6849]
[New LWP 6850]

warning: Could not load shared library symbols for linux-vdso.so.1.
Do you need "set solib-search-path" or "set sysroot"?
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
Core was generated by `/usr/bin/gnome-shell'.
Program terminated with signal SIGSEGV, Segmentation fault.

+ Trace 236478

(gdb) 

Note: I have autologin enabled. When I logout, gdm starts its gnome-shell instance.

Created attachment 332019 [details] [review]
Gracefully exit with failure if backend creation failed

Instead of continuing eventually crashing with a segmentation fault due
to a missing renderer, make MetaBackend an GInitable, and gracefully
handle the failure to fully create the backend with an EXIT_FAILURE.

Review of attachment 332019 [details] [review]:

LGTM

Attachment 332019 [details] pushed as 820a6ab - Gracefully exit with failure if backend creation failed