gnome-shell crashed at xcb_io.c:260: poll_for_event: Assertion `!xcb_xlib_threads_sequence_lost'' failed

[errors.ubuntu.com bug bridge]

[Impact]

This is the #1 crasher of gnome-shell in Ubuntu 20.04, though it's duplicated across multiple problem reports according to locale:

https://errors.ubuntu.com/problem/4de3d315d9df1c9699bda54beafeeeea8d52053c
https://errors.ubuntu.com/problem/2251b638f7a6167772f922dc5916740522c5c22b
https://errors.ubuntu.com/problem/943838b8a80c1da4f8df584b7d2ad3a13361fdd7
https://errors.ubuntu.com/problem/4b78bc9730e8681f0c42fc2ecea14d03544394f0

[Test Case]

None known. The plan is to just continue monitoring crash reports. Still, we are confident this is the fix because:

 * The offending source code in libx11 tells us it is :) and
 * The crash only started in Ubuntu with gnome-shell 3.34, which is the
   exact release in which XInitThreads was removed from mutter.

[Regression Potential]

Low. We add a single function call that tells libX11 to enable thread safety. This is the same as what we had in bionic, cosmic and disco, so it's well tested.

[Daniel van Vugt (vanvugt)]

This is actually the #1 (English locale) and #3 (Portuguese?) gnome-shell crash in focal this month.

https://errors.ubuntu.com/?release=Ubuntu%2020.04&package=gnome-shell&period=month

[Daniel van Vugt (vanvugt)]

The #1 crash link is unreachable:

https://errors.ubuntu.com/bucket/?id=/usr/bin/gnome-shell%3Agnome-shell%3A%20../../src/xcb_io.c%3A260%3A%20poll_for_event%3A%20Assertion%20%60%21xcb_xlib_threads_sequence_lost%27%27%20failed.

because of bug 1863689.

[Daniel van Vugt (vanvugt)]

If anyone experiencing this crash is reading, to work around it you should just be able to select 'Ubuntu on Wayland' on the login screen.

[Daniel van Vugt (vanvugt)]

Also tracking in: https://errors.ubuntu.com/problem/2251b638f7a6167772f922dc5916740522c5c22b

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Leperous (scabin)]

Had this after login, screen went black (cursor worked) for about 20 seconds, before the desktop recovered.

[Daniel van Vugt (vanvugt)]

Interesting thought. If this is the #1 crash then yes it would explain a lot of blank screen issues.

[Sebastien Bacher (seb128)]

Daniel, could you have a go to this one?

[Daniel van Vugt (vanvugt)]

Tracking in:

https://errors.ubuntu.com/problem/4de3d315d9df1c9699bda54beafeeeea8d52053c
https://errors.ubuntu.com/problem/2251b638f7a6167772f922dc5916740522c5c22b
https://errors.ubuntu.com/problem/943838b8a80c1da4f8df584b7d2ad3a13361fdd7
https://errors.ubuntu.com/problem/4b78bc9730e8681f0c42fc2ecea14d03544394f0

and that doesn't even include the top one (English) which has an unreachable link (bug 1863689).

[Daniel van Vugt (vanvugt)]

Fix for groovy proposed: https://salsa.debian.org/gnome-team/mutter/-/merge_requests/63

[Launchpad Janitor (janitor)]

This bug was fixed in the package mutter - 3.36.3-1ubuntu1

---------------
mutter (3.36.3-1ubuntu1) groovy; urgency=medium

  * Merge with debian, including new stable upstream release
  * debian/control: BD on adwaita-icon-theme 3.36.1-2ubuntu3.
    This version includes all the window decoration icons that mutter uses
  * Remaining changes with debian:
    - debian/control:
      + Update VCS flags to point to ubuntu salsa branch
    - debian/gbp.conf: update branch to point to ubuntu/master
    - debian/patches/x11-Add-support-for-fractional-scaling-using-Randr.patch:
      + X11: Add support for fractional scaling using Randr

mutter (3.36.3-1) unstable; urgency=medium

  * New upstream release (LP: #1881971)
   - Broadcast clipboard/primary offers
   - Fix monitor screen cast on X11
   - Implement touch-mode detecation for the X11 backend (LP: #1880596)
   - Drop external keyboard detection from touch-mode heuristics
   - Fix leaked DMA buffers in screencasts
   - Fixed crashes

mutter (3.36.2+12+gb425f1153-1) experimental; urgency=medium

  * Team upload
  * New upstream snapshot from the gnome-3-36 branch
  * d/p/backend-x11-Reintroduce-XInitThreads.patch:
    Drop patch, applied upstream

 -- Marco Trevisan (Treviño) <email address hidden> Thu, 04 Jun 2020 21:46:56 +0200

[Timo Aaltonen (tjaalton)]

Hello errors.ubuntu.com, or anyone else affected,

Accepted mutter into focal-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/mutter/3.36.3-0ubuntu0.20.04.1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-focal to verification-done-focal. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-focal. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Daniel van Vugt (vanvugt)]

Verified the fix is present in mutter_3.36.3.orig.tar.xz but as mentioned above, no known test case.

[Łukasz Zemczak (sil2100)]

The verification of the Stable Release Update for mutter has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

[Launchpad Janitor (janitor)]

This bug was fixed in the package mutter - 3.36.3-0ubuntu0.20.04.1

---------------
mutter (3.36.3-0ubuntu0.20.04.1) focal; urgency=medium

  * New upstream release (LP: #1881971)
    - Broadcast clipboard/primary offers
    - Fix monitor screen cast on X11
    - Implement touch-mode detecation for the X11 backend (LP: #1880596)
    - Drop external keyboard detection from touch-mode heuristics
    - Fix leaked DMA buffers in screencasts
    - Fixed crashes
  * Refreshed patches
  * d/p/backend-x11-Reintroduce-XInitThreads.patch:
    - Dropped (merged upstream)

mutter (3.36.2-1ubuntu1~20.04.2) focal; urgency=medium

  [ Daniel van Vugt ]
  * d/p/backend-x11-Reintroduce-XInitThreads.patch:
    Fix a very common crash when running in X11 (LP: #1877075)

 -- Marco Trevisan (Treviño) <email address hidden> Fri, 05 Jun 2020 19:29:32 +0200

[Dani (scrlk)]

I'm running mutter version 3.36.3-0ubuntu0.20.04.1 but I still have the same problem.

[Daniel van Vugt (vanvugt)]

The issue is continued in bug 1886059.