Probably a duplicate of bug 788607.

I hit the same assertion when I switch my screen off/on (Dell P2415Q HiDPI, NVIDIA Quadro 2000 using Nouveau, on Wayland). I have applied the diff of commit 6eb7d13 referenced in bug 788607. Unfortunately, this did not resolve the problem.

Created attachment 361300 [details]
Backtrace

Tbe problem persists with the following ArchLinux packages:

gnome-shell 3.26.1+3+g43ec5280b-1
mutter 3.26.1+7+g41f7a5fdf-1

Based on the git commit in the package versions, I'd assume the fixes from bug 788607 would be included.

However, one overlap I have identified with the comments from bug 788607 is that there is no problem when there are no open windows.

Created attachment 361462 [details]
libmutter.so null pointer dereference backtrace and regs

Null pointer dereference that still occurs with the folliwng packages on ArchLinux:

gnome-shell 3.26.1+3+g43ec5280b-1
mutter 3.26.1+7+g41f7a5fdf-1

The trace looks strikingly similar indeed, but where from in Javascript it came from is harder to determine.

Any way you can attach a gdb to the process and reproduce? Then when you hit the assert, run:

print gjs_dumpstack()

and paste what is printed to stdout/stderr. (note that it might end up in the journal).

Created attachment 361499 [details]
gdb log with JS backtrace

I've added a SIGSEGV catchpoint to invoke gjs_dumpstack(), but the JS stacktrace is empty (also note that there is no JS calls in the GDB stacktrace for the null ptr dereference).


Oct 13 11:57:43 hostname org.gnome.Shell.desktop[5852]: == Stack trace for context 0x55c289d52000 ==
Oct 13 11:57:43 hostname org.gnome.Shell.desktop[5852]: (EE)
Oct 13 11:57:43 hostname org.gnome.Shell.desktop[5852]: Fatal server error:
Oct 13 11:57:43 hostname org.gnome.Shell.desktop[5852]: (EE) failed to read Wayland events: Broken pipe
Oct 13 11:57:43 hostname org.gnome.Shell.desktop[5852]: (EE)
Oct 13 11:58:25 hostname org.gnome.Shell.desktop[6236]: glamor: EGL version 1.4 (DRI2):

Georg: your second trace (attachment 361462 [details]) looks more similar to mine in bug 788788. I will attach it here as well, it contains more symbols than your trace.

Created attachment 361502 [details]
Trace of NULL pointer deref in meta_logical_monitor_get_scale

I posted a USD 100 bounty at bountysource.com to get this fixed.

https://www.bountysource.com/issues/50257944-mutter-error-backends-meta-monitor-manager-c-2267-meta_monitor_manager_get_logical_monitor_from_number-assertion-failed-unsigned-int-number-g_list_length-manager-logical_monitors

The latest changes in the gnome-3-26 branch solve these problems for me. I still have to apply the workaround in bug 788788 though. With mutter from gnome-3-26 and that workaround I can reliably switch my screen off and on without gnome-shell/mutter crashing.

*** Bug 789040 has been marked as a duplicate of this bug. ***

Created attachment 361654 [details] [review]
window/wayland: Handle resizing when headless

We tried to get the geometry scale, which may depend on the main
logical monitor assigned to the window. To avoid dereferencing a NULL
logical monitor when headless, instead assume the geometry scale is 1.

Created attachment 361657 [details] [review]
ArchLinux PKGBUILD patch to include Jonas' working patch

Thank you, your proposed patch works and solves the issue for me.

I've included the PKGBUILD patch that I used to test this locally for Jan's convenience.

Thanks! I will try the patch as well tonight and report back.

Created attachment 361681 [details]
systemd journal of crashing after applying the latest patch

Zu frueh gefreut!

Seems there is another bug, this one triggered when switching the screen back on. And not a helpful backtrace. Doesn't always reproduce.

Created attachment 361682 [details]
backtrace of the last bug from gdb

Some more information to pinpoint the issue.

Could you install debug symbols, and get a full backtrace and attach that? Using gdb, that'd be the output of "backtrace full" on the core dump. FWIW, the new trace could be also be bug 788627 or bug 788908.

For me it works now: I can reliably turn off and on the screen without gnome-shell crashing. This increases usability significantly :).

There are some glitches though. After switching on the screen again, gnome-terminal windows are 1/4th of the size. Nautilus windows retain the same size but are lo-DPI and zoomed. After switching back and forth to another desktop all the windows are normal again.

Jonas, I applied your patch from https://bugzilla.gnome.org/show_bug.cgi?id=788764#c13 and it fixed the crash. Thanks a lot!

But I see other issue exactly the described by Daniel. I have a HiDPI monitor with scaling coefficient "2". After monitor resume terminal becomes scaled down to "1" and Nautilus fonts become blurred. I need to press "Super" button (show all windows at current desktop) to return to the correct state.

Created attachment 361801 [details]
another backtrace of the latest bug

Same bug with different backtrace this time.

I tried building mutter with:
CFLAGS="-flto=no -O0 -ggdb" ./configure --enable-debug …
But still didn't get any useful debug symbols.

Review of attachment 361654 [details] [review]:

lgtm

Comment on attachment 361654 [details] [review]
window/wayland: Handle resizing when headless

Attachment 361654 [details] pushed as 3572502 - window/wayland: Handle resizing when headless

Pushed to master. Marking the ARCH patch as "rejected" as I can't find any better patch status for it.