Cinamon lockscreen crash to blackscreen and recovery from it

Distribution

Mint 21.3

Package version

6.0.4

Graphics hardware in use

NVIDIA GeForce GTX 1060 6GB

Frequency

Only occasionally

Bug description

I had my computer running in lockscreen with screen turned off. After i came back some hours later, i only saw a black screen, but the mouse cursor was working.

I switched to a different terminal using Ctrl+Alt+F2
There i investigated the journal and found that a process did crash.
I didnt know what the process did, so i just copied its commandline from coredumpctl and run it again with the environment DISPLAY=:0:

DISPLAY=:0 /usr/lib/x86_64-linux-gnu/cinnamon-screensaver/cs-backup-locker --xid 94371854 --term 1 --session 7
X Error of failed request:  BadWindow (invalid Window parameter)
  Major opcode of failed request:  21 (X_ListProperties)
  Resource id in failed request:  0x5a0000e
  Serial number of failed request:  12
  Current serial number in output stream:  12

** (cs-backup-locker:122248): CRITICAL **: 17:58:13.266: cs_event_grabber_get_keyboard: assertion 'window != NULL' failed

** (cs-backup-locker:122248): CRITICAL **: 17:58:13.266: cs_event_grabber_get_mouse: assertion 'window != NULL' failed

(i only saw that it crashed again after i returned to that screen later to document my steps for this bug report)

I returend to the default screen on 7 and now my lock screen was back. I logged in. Cinnamon was in the "fallback mode" i pressed the button to repair that and now everything seems to be fine.

Steps to reproduce

It only happend once so far. I often leave my computer in lockscreen with turned off screen. It never happend so far.

1. Leave the computer running in lockscreen and screen turned off for a few hours?
2. luck?

Expected behavior

Its okay, if the lockscreen takes a moment or two after i turn the screen on to show up. But after a few seconds it should be there and i should be able to unlock my computer.

Additional information

I had a virtualBox VM running.

I was able to capture the coredump. An overview here, if requested i would be able to probe specifics, but i dont like to share a coredump publicly.

           PID: 79872 (cs-backup-locke)
           UID: 1000 ([redacted])
           GID: 1000 ([redacted])
        Signal: 11 (SEGV)
     Timestamp: Fri 2025-03-21 17:50:18 CET (21min ago)
  Command Line: /usr/lib/x86_64-linux-gnu/cinnamon-screensaver/cs-backup-locker --xid 94371854 --term 1 --session 7
    Executable: /usr/lib/x86_64-linux-gnu/cinnamon-screensaver/cs-backup-locker
 Control Group: /user.slice/user-1000.slice/user@1000.service/app.slice/dbus.service
          Unit: user@1000.service
     User Unit: dbus.service
         Slice: user-1000.slice
     Owner UID: 1000 ([redacted])
       Boot ID: 6e428318ed9648479b9a87084379a648
    Machine ID: aaa642a1efb049fba8d6ca0c8d22ff0a
      Hostname: [redacted]
       Storage: /var/lib/systemd/coredump/core.cs-backup-locke.1000.6e428318ed9648479b9a87084379a648.79872.1742575818000000.zst (present)
     Disk Size: 1.0M
       Message: Process 79872 (cs-backup-locke) of user 1000 dumped core.

[...]

                Found module cs-backup-locker with build-id: e2bfd517fa1927e0f4b989f0e1ed9e128affaa9b
                Stack trace of thread 79872:
                #0  0x00007f700d55e226 n/a (libgdk-3.so.0 + 0x65226)
                #1  0x00007f700d566191 n/a (libgdk-3.so.0 + 0x6d191)
                #2  0x00007f700d569d89 n/a (libgdk-3.so.0 + 0x70d89)
                #3  0x00007f700d52fa99 gdk_display_get_event (libgdk-3.so.0 + 0x36a99)
                #4  0x00007f700d569f46 n/a (libgdk-3.so.0 + 0x70f46)
                #5  0x00007f700d173d3b g_main_context_dispatch (libglib-2.0.so.0 + 0x55d3b)
                #6  0x00007f700d1c92b8 g_main_context_iterate.constprop.0 (libglib-2.0.so.0 + 0xab2b8)
                #7  0x00007f700d1732b3 g_main_loop_run (libglib-2.0.so.0 + 0x552b3)
                #8  0x00007f700d848d2d gtk_main (libgtk-3.so.0 + 0x248d2d)
                #9  0x000055c1501282c8 n/a (cs-backup-locker + 0x42c8)
                #10 0x00007f700ce29d90 __libc_start_call_main (libc.so.6 + 0x29d90)
                #11 0x00007f700ce29e40 __libc_start_main_impl (libc.so.6 + 0x29e40)
                #12 0x000055c1501283e5 n/a (cs-backup-locker + 0x43e5)
                
                Stack trace of thread 79875:
                #0  0x00007f700cf18bcf __GI___poll (libc.so.6 + 0x118bcf)
                #1  0x00007f700d1c9256 g_main_context_iterate.constprop.0 (libglib-2.0.so.0 + 0xab256)
                #2  0x00007f700d1713e3 g_main_context_iteration (libglib-2.0.so.0 + 0x533e3)
                #3  0x00007f700d171431 glib_worker_main (libglib-2.0.so.0 + 0x53431)
                #4  0x00007f700d1a2ab1 g_thread_proxy (libglib-2.0.so.0 + 0x84ab1)
                #5  0x00007f700ce94ac3 start_thread (libc.so.6 + 0x94ac3)
                #6  0x00007f700cf26850 __clone3 (libc.so.6 + 0x126850)
                
                Stack trace of thread 121276:
                #0  0x00007f700cf18bcf __GI___poll (libc.so.6 + 0x118bcf)
                #1  0x00007f700d1c9256 g_main_context_iterate.constprop.0 (libglib-2.0.so.0 + 0xab256)
                #2  0x00007f700d1713e3 g_main_context_iteration (libglib-2.0.so.0 + 0x533e3)
                #3  0x00007f700d36b24d g_subprocess_wait (libgio-2.0.so.0 + 0xb324d)
                #4  0x000055c1501293d1 n/a (cs-backup-locker + 0x53d1)
                #5  0x00007f700d36a194 g_task_thread_pool_thread (libgio-2.0.so.0 + 0xb2194)
                #6  0x00007f700d1a5714 g_thread_pool_thread_proxy (libglib-2.0.so.0 + 0x87714)
                #7  0x00007f700d1a2ab1 g_thread_proxy (libglib-2.0.so.0 + 0x84ab1)
                #8  0x00007f700ce94ac3 start_thread (libc.so.6 + 0x94ac3)
                #9  0x00007f700cf26850 __clone3 (libc.so.6 + 0x126850)
                
                Stack trace of thread 79876:
                #0  0x00007f700cf18bcf __GI___poll (libc.so.6 + 0x118bcf)
                #1  0x00007f700d1c9256 g_main_context_iterate.constprop.0 (libglib-2.0.so.0 + 0xab256)
                #2  0x00007f700d1732b3 g_main_loop_run (libglib-2.0.so.0 + 0x552b3)
                #3  0x00007f700d3cd81a gdbus_shared_thread_func (libgio-2.0.so.0 + 0x11581a)
                #4  0x00007f700d1a2ab1 g_thread_proxy (libglib-2.0.so.0 + 0x84ab1)
                #5  0x00007f700ce94ac3 start_thread (libc.so.6 + 0x94ac3)
                #6  0x00007f700cf26850 __clone3 (libc.so.6 + 0x126850)
                
                Stack trace of thread 79886:
                #0  0x00007f700cf18bcf __GI___poll (libc.so.6 + 0x118bcf)
                #1  0x00007f700d1c9256 g_main_context_iterate.constprop.0 (libglib-2.0.so.0 + 0xab256)
                #2  0x00007f700d1713e3 g_main_context_iteration (libglib-2.0.so.0 + 0x533e3)
                #3  0x00007f700d36b24d g_subprocess_wait (libgio-2.0.so.0 + 0xb324d)
                #4  0x000055c1501293d1 n/a (cs-backup-locker + 0x53d1)
                #5  0x00007f700d36a194 g_task_thread_pool_thread (libgio-2.0.so.0 + 0xb2194)
                #6  0x00007f700d1a5714 g_thread_pool_thread_proxy (libglib-2.0.so.0 + 0x87714)
                #7  0x00007f700d1a2ab1 g_thread_proxy (libglib-2.0.so.0 + 0x84ab1)
                #8  0x00007f700ce94ac3 start_thread (libc.so.6 + 0x94ac3)
                #9  0x00007f700cf26850 __clone3 (libc.so.6 + 0x126850)

Start with the cs-backup-locker executable and the journal/coredumpctl evidence supplied in the report, then investigate the BadWindow and failed event-grabber assertions. Done means the locker no longer crashes after the display has been off for hours and the user can return to and unlock the normal lock screen.